First you want a healthy rabbit. Check them all over for runny noses, weepy eyes, signs of mites, dull coat, tooth problems and other issues. If more than one of the rabbits seems to have issues, then you might want to reconsider that litter or source as the rabbits will probably need vet treatment which can be costly.
As far as personality, you should have an idea of what you want. If you can, sit in an enclosed space with the rabbits. If they are form the same litter, then have them all together. See how they react the each other, you and a new environment. You can pick the first one the comes up to you and lets you pet/handle them or maybe the one that takes a bit longer to warm up but seems to be more friendly once it gets to know you. You can also just go for that one that you like. If you want a specific sex, then try to only have those ones in the pen. You know what you are looking for, so go with how you feel about it. Sometimes you just have in immediate connection with a rabbit.
You can try making some noises and doing some quick movements to see how they react and how they recover if they are startled. Move your hand around in front of their face to see if they will follow it or are interested or shy away. Also try petting them to see if they like it, want more or want nothing to do with it.
Keep in mind that you are getting a young rabbit. The personalty can change as they get older. There is no guarantee that a friendly rabbit will stay that way as it gets older. Shy rabbits can blossom and become great pets. I would go for a rabbit that you have a connection, without a good connection a relationship can be harder to form.
