I've tried a BB, Treo, various Nokia, iPhone, and samsung qwerty keyboards.
The only one that didn't suck was the Nokia E71 (I didn't try the E90 though).
They have the wrong feel, they have sub-par layouts, etc. The G1 is, IMO, orders of magnitude better. I like the key feel, I like the level of tactile feedback, etc. I like that the keys are staggered, like a real keyboard. The only thing I find lacking in the keyboard itself is that there's no control key, and no escape key (making ConnectBot have to do special things to achieve that).
I don't know if dskyers meant (by "offset") the part about the keys being staggered like a real keyboard, or that the device itself is asymmetric (chin on one side only). For the former, like I said, I think that's a bonus, not a minus. For the latter, I think that's a problem with the device not the keyboard itself. (I do wish that either there were 2 chins, like a sidekick, or that it was chinless, like an HTC Touch Pro, or the above concept).
But, IMO, the keyboard itself is one of the things that the G1 got amazingly right. I could make tradeoffs on the rest of the phone, but not the keyboard -- anything less would be very bad.
As for on-screen keyboards.. my only wish is that you could do T9 type input, for sending SMS, using the existing on-screen dialer. Otherwise, I find virtual qwerty keyboards to be worse than useless. Especially the iPhone's.