I'll chime in, as I've toiled over this very topic for too long. For now I think I've solved my puzzle after picking up the Tenba large messenger bag. I fly a LOT, so efficiency is the name of the game (no checked luggage). I have a roller that houses my clothes, necessities and tripod The rest of my gear and laptop in my Tenba large messenger. I don't want to wrestle with a loose tripod and my Slik Pro 340DX fits perfectly in my roller carryon. I've never once had an issue with TSA.
With my two carryon bags (roller, and Tenba), I have my tripod and a lot of gear. To give you an idea: For this trip I brought my 50D, 15" laptop, Sigma 50-150, Canon 100-400, Sigma 50 1.4, Canon 15-85, 430EX flash, extras + my Archos 5....(highly recommend for anyone who travels a lot...2 big thumbs up!).
What I like about the Tenba bag, is it eliminates an extra bag for me. I typically I pack my gear in one bag, and stash my "walkaround" bag in my larger carryon. The Tenba's big enough to bring a substantial amount of gear to get you to your destination, yet small enough to "work out of" once you get there. I don't like shooting out of a backpack, so that wasn't an option for me. I live with a laptop bag on my shoulder, so the Tenba feels right at home for me, and the THICK large padded shoulder strap is really, really nice (not mentioning other features).
I concur that there is no "perfect" bag, although my current travel setup is not far off from perfect for my needs. Can't wait to use it on my trip to Cozumel in 3 weeks!

