I started out with Drive Hud fairly inexpensive and it works ok but I found it really difficult to perform certain tasks other than what they have pre- programmed.
I most recently purchased Holdem Manager 3 and it was tough to learn and am still learning but I am not computer savvy. It's a bit more $$ plus it won't work on Betonline unless you purchase a card catcher for additional $$ But it is a fantastic Hud.
Jonathan Little from PokerCoaching.com has an excellent HM3 presentation on youtube.