I think it's already been said but HTC mail is a just skinned stock Android mail app. And the stock Android email app sucks. Gmail is far superior partially because it's tailored for use with Gmail. As for generic pop3/imap mail I use k-9 because well...it doesn't suck and has most of the features you'd probably want in a standard mail receiver.
K-9 saved my butt. I spend four hours (I mean it) with help from VZW phone support trying to set up my POP3 accounts and failed. Had to go to the store, the guy downloaded K-9, and everything worked.