I also have a Kata 3N1-30 sling back / backpack hybrid which is also very nice. It's larger than the LowePro SlingShot 200 AW, allowing me to carry my mounted Nikkor 24-70mm f/2.8 with its lens hood attached in its forward position (I have to attach the hood in reverse position to fit it in the SlingShot 200 AW). This is a very nice bag that will do either right-side or left-side sling carry (the SlingShot 200 AW only goes one way, strap over the right shoulder, and swung around left) and it acts as a full backpack, too, when you untuck and anchor both straps. As nice as this bag is, however, it just doesn't (in my opinion) have the build quality that the LowePro products have--it doesn't feel as bombproof to me. I picked up a Kata for when I need a larger sling bag than the SlingShot 200 AW, but am now thinking of selling it, and picking up a LowePro SlingShot 350 AW to replace it instead. (Another key advantage to the LowePro "AW" products is that the all-weather cover is affixed to the bag, so is easier to both use and put away. The Kata has a detached all-weather cover.)
For when I want to carry everything, I have a LowePro CompuTrekker Plus AW backpack. This pack is huge--much larger than the photos of it alone would indicate. I use this bag for heavier travel, and also as an office-on-the-go. (Here's a photo of my CompuTrekker Plus AW pretty well packed up.) I can fit my entire mobile office in here, and pretty much all of the photography stuff I currently have. If huge is what you're looking for, this is really a wonderful piece.
Again, in my experience, it's hard to go wrong with LowePro gear. Everything I've owned by LowePro (from compact camera cases to the huge CompuTrekker Plus AW) has been impeccably constructed, and well thought-out for its intended purpose.