Upload & Sell: On
Sigh... I can't believe I've spent over $1k on backpacks, holster bags, belts, roller bags... this is getting to be a bit much.
Anyway- my LowePro Slingbag 300 AW is good. The AW w/ any LowePro product means that there is a rain pouch. The plus to it is that it's very easy to move to in front of you so that you can access it easily. The drawback is that w/ only 1 strap, it tends to wear a bit on 1 shoulder, though this is reduced if you use the belt that goes around your chest.
You may also want to consider a system by ThinkTank- something like a Digital Holster to hold the camera + 1 mounted lens, then 1 of their modular belts so that you can add/subtract items as necessary.
The LowePro Flipside is great for crowds because when you put it on as a backpack, the zipper touches your back, so that thieves can't get to it unless they get you to take it off your back. But it doesn't hold as much- always a tradeoff.
I would HIGHLY recommend going to a store w/ your gear & seeing what works best for your situation.