I've only ever used handcent (I think I downloaded it on the way out of the verizon store, actually), but I love the fact that we have a choice. I think that Google did the right thing there.
I downloaded Chomp a while ago but I wasn't a fan. Granted, I didn't give it much of a chance; and perhaps I would like it more if I really got to playing with it and customized it the way I wanted.
I will say, though, that if Chomp doesn't eat (see what I did there?) random text messages like handcent has done for me (albeit rarely, it has happened; most recently on a message from my mother concerning my pregnant wife) then that fact alone might be enough to make me switch. I will give it an honest try and see which one I truely like better.
Honest opinion after using Chomp for ~2 hours straight:
Decent. Wish it had more conversation styles, but I use the bubbles in Handcent too, so I like them.
Notification vibrations - Prefer the 2 short vibes from Handcent to the one long one in Chomp SMS, And the other options I saw there weren't any better.
Customization - Handcent has a slight edge (in my mind) with the ability to customize to 4 different styles. Don't get me wrong, there's a lot of tweaking options available with Chomp, and I like the simpler style of changing colors that chomp has.
Deal breaker (for me) - Chomp SMS is not able to set different LED colors for different contacts like Handcent is. That's a deal breaker. I like to glance at my phone and know if the vibration I just got was a generic text or my wife.
Just my opinions. If Handcent really did get their random message deletion issue fixed (claimed to have done so in the latest update notes) then it wins for me. Chomp SMS is close, but not there yet.
+1 Laramie