Is doing degree after diploma worth or after 10+2?

There is not much difference for you as you want to go for Engineering degree only after diploma also. The difference comes to you in your understanding of mathematics and sciences. In 12th class, you will get a good understanding of mathematics and sciences. Even in 1st year engineering, you will get some knowledge of mathematics and sciences. So you will understand the theory behind the engineering subjects.
After the diploma, you will get admitted to the 2nd year of Engineering. In your diploma also you will not get that foundation in mathematics and sciences
Many Organisation prefer student who followed the pattern of 10 + 2 + 4 more than 10 + 3 + 3. I observed this tendency in many organisations. They feel the mindset of people who did a degree after diploma will be different from that of people who did a degree after intermediate. There are some government jobs also which will ask fo 10 + 2 + 4. 10 + 3 + 3 pattern students will not be eligible to apply for these jobs.
Keeping these facts in mind probably some of your relatives told you that degree after 12th is better than degree after diploma.

Thanks Sir

In general, people would like to pursue Engineering Degree after 10+2 only and fewer percentage goes with 10 + Diploma + Engineering Degree.

One of the most important reason is, employment opportunity after the Engineering Degree. Most of the employers preferring and accepting the candidates who had completed the Engineering Degree after 10+2 pass-out with better percentage.

Only few employer prefer or specially mention on their adv as they would like to hire those applicants who had completed Engineering Degree after 10+Diploma pass-out.

Very few Diploma has value in real that has to be completed after 10th exam pass only. It is quite different from the other.

Few foreign employers prefer Diploma candidate rather than Degree holders for the same subject discipline. Here and there little different story for sure on the education and talent perspective.

Whatever rout you approach for the completion of engineering degree in computers either 10+2 followed by writing the competitive test to be inducted in the engineering college or taking a diploma course from a recognised polytechnic and later persuing the degree course in engineering, there would not be difference in the time consumption. To explain the same, supposing you have chosen the path of taking admission in the engineering college, your total timing for the course would be 10+2+4 = 16 years where as after passing your class ten and then joining a polytechnic for diploma, the total timing would be 10+3 years in completing the diploma. In the later situation, if interested for the degree course in engineering, you will be admitted in the second year of 4 year engineering course. Hence the total time span in this case is also 16 year from your class one.
However, your conception in both Physics and Mathematics would be better while undertaking 10+2 course because of the elaborate studies of the different chapters helping you to understand your degree course at ease since there is always application of both the subjects in your engineering curriculum. An aspirant undergoing for engineering degree course after diploma would be lacking that proficiency unless one takes a personnel coaching in these subjects to strengthen ones fundamentals. This would be an additional task for such aspirants doing engineering after one's diploma.

Engineering degree after the completion of the diploma course has its own advantages. A diploma in any branch of engineering is considered equivalent to a pass in the intermediate examination. In case someone wants to go for a job after diploma, he has the advantage of applying for jobs that require a diploma as a qualification as well as intermediate qualification.
The student who completes a diploma in any branch of engineering and takes lateral entry into engineering degree course will have the advantage of the technical knowledge he acquired during his diploma course. It will be easier to understand the subjects as already they were dealt with in the diploma course. One can come out with flying colors in the engineering degree course.
The expenditure involved in getting an engineering degree through lateral entry after the diploma is lesser than the other route of doing an engineering degree after intermediate.
The competition is also less in the case of lateral entry to engineering course after a diploma. The number of candidates appearing after intermediate for the entrance examination of engineering runs into lakhs and competition is heavy.
Considering all the above points, it is easier to get admission into an engineering course after diploma, the expenditure is less, and can be in the top rankers in the class with the knowledge already gained. If you have already joined the diploma course, continue without any hesitation. Do not bother about what your relatives and others say.
The intermediate marks are relevant only up to your entry into the engineering degree but not anymore.

Most of the people prefer 10+2+4 pattern rather than 10+3+3. In many jobs degree, after10+2 is more in demand. If you are doing a degree after diploma then It is quite different from diploma after degree. Doing diploma after 10 +2 has not much value in career-making. it is very few in demand but everything has its own advantages.
Those students who pursue a diploma in any branch of engineering feel easy in understanding further engineering degree course. As already discussed technical point during diploma course. Moreover, it will be easier for you to get admission into engineering after diploma. And there would be a great chance of less expenditure in doing a degree after diploma.
Considering all pros and cons of education pattern, I would suggest you go for a degree after 10+2.

There are some employers who may consider the 10+2+ Engineering students better than the 10+2+Diploma+Engineering students but that varies from the organisation to organisation and is not a universal criterion for acceptance of the candidates in some vacant position in the organisations. So, I do not think that one should worry for that aspect. In fact the real job situation today is very tricky and some diploma persons are better placed in getting a job then the engineering graduates. This is more true in self employment potential which is quite good in case of Diploma holders.

Another thing which is of more importance is that how one fares in the final engineering exam. That score is of utmost impotence and if one is able to excel there than no one will bother as one has come from direct route or Diploma route. So, what I will advice is that whichever route one chooses one has to keep the final engineering exam merit in ones mind and make it an objective to do best possible there and then many doors of career in industry will open. It is not only the technical job after the engineering but there are so many national level examination in central Govt, Railway department, State level administrative jobs, and other competitive examinations where one can definitely qualify if he had fared well in the engineering. It is a well known fact that the academically good students can fare well everywhere.

We are today in an environment of skill based knowledge and if one has adequate skills one can definitely rise in ones career. So, try to learn skills as much as possible related to your core area and success would come to you naturally. Any student who is doing well in his exams and learning skills to perform the task efficiently will be accepted by any employer and his job swapping potential will be quite high and employer will take his exodus from the company seriously and try to woo him with more perks.

After Diploma, you can join Engineering via the lateral admission, direct to the second year of the four year Engineering course. So in effect the number of years spent via both stream is same. But in relation to jobs a person with Diploma background has more practical job orientation than the more theoretical orientation of one who came via 10+2 route. Sure, there will be slightly a small disadvantage for diploma -lateral entree student as he may not be theoretically sound in Mathematics. But with a little focus and effort this also can be overcome easily.

It only matters ho you complete your Engineering course. If the grades are good, then with the better job oriented attitude the job prospects can be more.