While I don't hate the Venture brothers, I do find them to be the least comedic characters on the show. I agree that the're more of a catalyst for the plotlines, hence less time is devoted to their characters than most of the supporting characters (which really make the show as brilliant as it is!)
The Monarch is hands down the most hysterical character on the show (and perhaps on any show), with Orpheus and Sampson closing in right behind him. I'm astounded at how great this show is and how it keeps getting better. It saddens me to think that season 4 will be the last, but I suppose it's better to call it quits before the show runs out of steam which is something some other shows can't seem to manage (Simpsons, I'm looking at you!).
Thanks for the heads up on the t-shirt club. While I can no longer wear t-shirts to work, there's absolutely no way I could deny this one. The Guild shirt is worth the price of admission alone!