Yahoo gives you far more storage space and the bulk/junk mail folder and trash bin do not count towards your limit.
MSN have been promising hotmail users a bigger inbox (currently 2000kb) for a while now.. the last e-mail said.. "in the autumn".
Gmail is better than all of them. It is currently in testing and you can only get in with an invite. But soon you'll be able to sign up =)
By the way, Gmail gives you 1gb of storage.