Both are good and have advantages for preparing NEET/AIIMS Exams. But the thing is the most effective way to prepare is to join Offline course first and then go for Online course. This will clear your concept more deeply.
The one thing is very important is you must join online test series from any companies because you know exams will be held online from next year.
You can join online test series by AAKASH, ALLEN, Careerpoint