No moonlit walks on the beach T?
Best bet... see who you mesh with in the first day or so of training. Whoever you choose as your SIM Partner is a good person to room with since you two will be on the same schedule. It sucks to room with someone who has an opposite sim schedule... You'll be trying to sleep while his alarm is going off at 2am and he's banging around in the shower... and vice-versa during the day.
Once you pick your sim partner... then just switch rooms. There will be a lot of that going on during the first week.
...and like rigger said above... don't forget to request a fridge the moment you check in!
Bob