After diploma completion which was the better to go like BITSAT and ECET for engineering

No, you cannot get admission in B.Tech Second year in BITS, Pilani campus because the institute does not offer admissions through Lateral Entry Scheme. Candidates who have completed 12th standard with PCM from a recognised board and who have qualified in BITSAT entrance examination are eligible to get admission in BITS campus. So, you cannot get admission in BITS campus by appearing for ECET entrance examination and the college option will not be available at the time of ECET counselling process. So, I suggest you to appear and qualify in ECET exam with good marks, then, you can directly get admission in B.Tech Second year in top colleges equivalent to BITS campus.