I have secured 94.31 percentile in b.arch whereas 84.16 in mains so which one of them is better?

The prospects are good for both, however considering your percentile for B.arch you might end up getting a much better college as compared to the college and branch that your JEE percentile will fetch you. Lastly do keep in mind the following points, this will help you in taking a more informed decision.

• At your percentile although you will get a good college to do your architecture, you need to be passionate about it, because architecture is a unique blend of both creativity and engineering. Therefore, it is more rigorous as compared to engineering.
• Also before taking up architecture remember that it's a field where you need start carving out a career path all by yourself initially before you land into good paying jobs.
• Now coming to your JEE percentile there are two options for you, either you will end up getting into some of the best NITs but you will get a lower branch or you will land into the new NITs in a good branch, I won't suggest you to go for the former since it will do nothing good but will make you conprocomp on your passion whereas the later is a better choice but the struggle will be similar to pursuing a B.arch.
• There is very high possibility that at this JEE percentile you might not even get into a good private college. So your only best option is to go for B.arch, in the given circumstances.

So these are your options and the path ahead based on what you choose.