I think you'll find as many answers to that as there are riders. Seems like alot of people like the the Airhead BMW's for their simplicity. Glen is riding around the world on the BMW 650GS, but previously had a KLR650. There's a husband/wife on a R1150GS and a 650GS. There's also a couple on the KTM 640s. Guess it depends on the type of riding you like to do and how much you want to pack. The beemers are better for sticking to the pavement, where the KLR/KTM might be better off the beaten path.
As far as weight goes, the best thing to do would be to upgrade your suspension. Usually when you get it built they take into account rider weight, type of roads you intend to ride and amount of weight you plan on carrying. As long as you can keep most of your luggage as close to the passenger area as possible you should be ok. I just wouldn't carry more than the weight of an average person back there. That gives you at least 150 pounds to deal with, which should be more then enough.
Errin