I've used a Lowepro Slingshot 200 extensively (ie EVERY shoot) for the last 2+ years with the exception of long and/steep mountainous hikes where too much other non photography gear is also necessary to be accomodated in a full backpack. I use it in a somewhat unorthodox way, ie I gutted out all of the velcro partitions. While I store my camera in the Slingshot between shoots, in the field the camera is worn around my neck and at-the-ready. Whatever other gear I'm bringing fits inside the Slingshot's compartments. Lenses are stored in their Lowepro LensCases. If occasionally I'm torn as to which lenses to limit myself to, I can always strap on 1-3 LensCases to the Slingshot's exterior via the wonderful SlipLok system integrated into both the Slingshot and LensCases (and all/most other Lowepro gear). I've heard other people complained about the weight being borne on only one shoulder, but I've carried mine for miles and hours (all day) and while the weight was noticed, it wasn't uncomfortable. The 300 would be good but probably would be too tempting to be overloaded. My adult sons also have 200's and love their's as well. Removing the partitions allows me great flexibility and access re which lenses/gear I bring. Reconfiguring partitions would drive me nuts!