It is what it is. As a big gundam fan I'd be very interested to see what is the communities favourite gundams and maybe even see some new ones that I haven't seen before.
You can only choose 1 but can give honorable mentions to others.
For me it's the Hydra Gundam. I first saw the gundam in gundam battle assault 1 and it was just so much cooler than any gundam I'd seen thus far. It was a fitting boss, I only wish it had made it into the Gundam Wing main story as Treize's final gundam.
Honorable mention goes to