Go SMS is the best. I've been an Android user since the G1, and I've used Chomp, Handcent, and Go SMS. It can do everything Handcent does, with a cleaner and crisper feel. Pop up is very crisp ... no lags or slowdowns. Tons of customizations (all the same as Handcent), plus pre-made themes that are awesome (they're even animated) as well. Love it!