I'm sure there is some goodness in training for both those lengths, although probably best to base it around the actual fight time.
If you're a beginner then start training with two minute rounds. Stay fairly intense throughout those 2 minutes and keep your technique as sharp as you can. 2 minutes of that will definitely be long enough. Once you outgrow two minute rounds with your fitness then start using 3 minute rounds.
I've changed the timer from 2 minutes to 3 minutes several times and chuckle as I watch the rest agonize through the last minute of each round. I didn't think it would make a big difference, but I guess it does.
I prefer doing 2 minute rounds but with 30 second rest, that way I can go full out for the full 2 minutes and I feel I get a better workout off it
Do 3x minute rounds. If you do novice fights the rounds will be 2 minutes long, but you will be ready for that by training for 3
Always did 3 minutes myself. Still felt gassed most of the time. IMO, you can't really overdo it. Rounds during actual fights are always going to seem longer than whatever you spar at.
Bingo. When I'm sparring, the round length generally gets changed without me knowing, I prefer it that way.