Mark, you are right about having that third gear for heavier guys. Next year when you and I train up for (and complete) the Triple By-Pass century ride up Loveland Pass, Vail Pass, and one other mountain pass, we’ll be glad we have it. We’ll probably be in the lowest gear the entire time.
For anyone who doesn’t live in a mountainous area, I’d lean more toward the double crank. Try asking if the bike shop will let you test ride a double and triple crank for a couple days so you can really get a good feel for the difference. However, you aren’t really saving that much weight with a double crank so if you are at all worried about being able to make it up hills okay, a triple crank is probably your best bet.
Either way, enjoy the ride.