I'll leave you with my little spreadsheet I used when making my purchase decisions.
Please note, you may completely disagree with my notes, and my measurements may not be exact. I made this for myself, but if you find it useful, all the better.
https://docs.google.com/spreadsheets/d/1iNdnnQ5ycZ88Hexw9ZQ8rmocqZd9ZRXHC0SL4WLLvqc/edit?usp=sharing[edit] I ended up buying and returning the Rival 600. It was too long, and it didn't work well with my claw grip. The right side is sloped the wrong way, so it just slides out of my hand. The shape of the back made it a bad shape for my claw/fingertip hybrid style. If you palm, this might be a good shape, otherwise I'd avoid it.
I bought and still use the MasterMouse S. After disassembling it and removing the stupid weight on the underside of the shell, it's a very light mouse. The length is very similar to the Logitech G9 I replaced, but the grip width is very small. If you have large hands, this is probably an immediate no-buy. I have a medium-sized hand length-wise but a large hand width, so I need something short and fat. This isn't it, unfortunately.
I've got my eye on the Logitech G Pro Wireless. Given the price, I want to get my hands (literally) on it before I drop that kind of cash.