For bionic. I just use stock. Nothing is wrong with it speed-wise. I like the little add-ons like extended power menu and such. But I was able to find mods or edit my own stuff to make stock exactly how I want it. For details on what a ROM has over stock, just check out the OP for that ROM. I tried Liberty and Th3ory and they're awesome, I just went back to stock for personal preference reasons.
If you realllly want a ROM...
Liberty has been the best by far for other devices I've owned. Its officially released for the bionic but its still in development a little bit.
Th3ory's ROM for the bionic is a moster as well, he's a beast.
Whoever named the Orange, must not have thought about the Carrot.
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