[oingo123]

I have used SEVEN (sprint mobile email) for over 3 years and think it is great. Lag time has been seconds. It is the only service I have found that can convert everything into push email from their servers.
Hotmail
Gmail
Imap
Outlook
Additionally, you can let SEVEN read your old pop accounts to simulate psuedo push email - let their servers check your pop email & only push it when you have something new. It is better than having your device do pop.

That said, I have noticed some battery drain on the HTC. If I remove it from the windows\startup folder and reboot the phone does last longer. I'm not sure which push email solution (if any) will give the best battery life.