I say "offen", but since I've been paying attention to how native speakers actually pronounce it, both ways are common and acceptable.

Either is ok.

often can be pronounced with or without t both are correct but for me, i don't pronounce the t i think it's easier without t

According to dictionary.com, either is correct. In school we were taught to NOT pronounce the "t", however, there are very many people who use the "t" and would think nothing about it if you use it.

you should not pronounce t in often if you want to talk like a native.