I have played Bomberman since I was little but now I would like to upload some speedrun even if my time is not ideal. But I don't have an NES right now. Is it legal to use an emulator? or do I need the NES or famicom? If I can use the emulator, which emulator is considered the most accurate?
There is nothing much that could stop you speedrunning on emulator if you would like to. Not like the game would simply self destruct to prevent you speedrunning, lol.
But that means the question is more 'would it be accepted' and that depends on the community you play with. Usually games from the NES/SNES/N64 era don't really mind because load times were already instant and having a computer blow the game out of the water doesn't save you frames. (or a noticeable amount).
And the biggest community for speedruns, speedruns.com, doesn't give anything about outlawing emulators. There is even times on the leaderboards that are marked as done on emulation.
So with all that said, pretty sure that you can speedrun on an emulator with no issues.