I love the layout of K-9 and wish google would implement something similar, or buy out K-9. Its much better than the stock gmail client imo as far as the interface ect go.
I use the IMAP IDLE settings in K9 for my Gmail account. It uses far less battery power in my opinion, so I'm leaning towards K9 (also, Gmail won't let me send attachments like MP3's and stuff, or let me download them lol).