My initial impressions are
Pro for Kiboko 22L
1. The straps are nice, the waist strap of the Kiboko 22L takes weight off the shoulders straps, which the waist strap of the TT Streetwalker Harddrive doesn't seem to do very well.
2. The accessory pockets are more numerous and larger. I like that I can put a travel tripod in the right accessory pocket (the left one is more compartementalized and designed for wallet, pens, keys, etc). Previously with my Thinktank I had to put the tripod inside the main compartment, thus really reducing the space in the main compartment for camera gear. But then again, most people don't have a 1.5 lb carbon fiber travel tripod.
3. I haven't tested it, but I have a feeling that Kiboko will be more comfortable on a long hike with a heavy load, given the better adjustability of its straps, load lifting straps, and decent waist strap.
4. I like the butterfly design, so I can load one half with camera equipment, and the other half with non-camera equipment, or potentially water, with less concern of it getting onto the camera equipment.
Pro for Thinktank Streetwalker Harddrive
1. Laptop compartment is easier to access. The Kiboko, you have to undo 2 clips to access it.
2. Overall, simpler. And cheaper.
3. Place for a large tripod.