Hello suhail,

It depends on following things 
1. Your interest. 
2. Your future plans. You want job or further studies after bsc. 
3. Current academic situation in your 1st year 

Firstly i want to tell you my friend you should take a decision precisely such that you don't have to regret later. I appreciate that you asked the question at right time in your life. I think if you interested in doing engineering then only go for diploma (polytechnic). A polytechnic degree will land you at an entry level job. If you are talking about value then i will say bsc. Degree is of greater value than polytechnic diploma but again it depends what you are actually upto after degree/diploma and in which field you are doing your bsc. 

'For higher studies in future' 
If you are planning for further studies(msc./mba) then you should go for degree because it adds good value in your overall career background than a diploma. 
My friend first decide what are your goals in life and make a quick decision before time flies.

All the best.