I agree with KC135. I assume that the class is going to be training, but either way, I think that the following comment will be relevant.
The purpose of training is to allow you to become more familiar both with your weapon and with proper tactics. Since the actual firearms are not going to be allowed, airsoft is probably the next best thing. However, buying an airsoft of a gun dissimilar to the one you will/do carry is pointless in helping you train for the real thing.
Now as for what brand to buy, I have no idea.