My top pick would be the Fuji GA645zi, which is perhaps the most advanced medium format film camera ever made. Plus it's also a super-handy grab 'n go package. But I don't think you can really go wrong with any of the GA-series cameras.
The 6x9 cameras handle nicely and they're not too heavy for what they are, but they are large. And in order to exploit all that the optics and the big negative are capable of, you'll want to hold the camera extra steady. Note that if you buy the 6x7, 6x8 and 6x9 cameras from Japan they may have high mileage, as these were popular for group photos at scenic spots (which is why they also have provisions for 4-exposure rolls of film)