I'd give you advice but I haven't had a mouse feel just right in years, sadly.

I have a claw grip mouse called the CM Storm that is great in my hand, but the build quality is super low, which annoys me to no end. My other mouse is a Deathadder which is slightly too large for a comfy claw grip and gives me cramps eventually, but the build quality is great.

Wish I had a decent compromise.

This one, though I guess it technically IS available, but $220 for a mouse that used to cost only $30 (thereabouts... don't remember) is a bit steep.

I looked at the Kensington Expert Mouse... I don't think I could get used to that. I prefer the wheel being under the thumb, but that design seems to be disappearing.

EDIT: I would fix the old Trackman I have, but I can't get the button to stop double clicking when I'm just doing a single click. This grew more frequent until I had to find something else.

Left or right handed?

I've had good luck with Logitech the last few times around. The current G500 works nicely.

For actual advice, try to get your hands on as many as you can.

Right.
I've had good with them until the Logitech M570.

I've been going to stores to try them out, but they mostly have wireless out for trial, which I don't want.

Yeah, wireless seems to show up at the stores a lot but at least you can try out the feel in your hand, assuming other mice share the same chassis and shell.

Ah, that one. Looks like they did stop production on it.

You could always try eBay for a used one or to use it for parts.

I was actually going to suggest the M570. I have no hand cramps with my M570, and I did have the other trackball you had a long time ago. I also still have the wireless version of the old one still, but I haven't located the receiver in my pile of computer cables and junk. I would really like to find my wired version, as wireless is pretty stupid for an input device that never moves and Logitech refuses to make a new wired one.
All Mice except for some weird shaped Microsoft Comfort mouse gave me hand cramps after 5 minutes. I still have that comfort mouse, but hate plugging it in because of the humongous receiver that would be hanging off my laptop.

Decided to try this out and just got it today (despite Amazon / LaserShip "delivering" it on September 18th... would have been nice if they had actually TOLD me).

I like the DPI-adjustment even though I haven't needed to try it out on anything yet. I can imagine how it would be useful in some applications.

Does seem a bit high-arched to me, though, so I'll be keeping the box for awhile just in case.

Thanks for the suggestions everyone. Too bad multiple posts can't be marked as solutions.
I'll likely try the Razer Deathadder for my home computer once the mouse it has now dies.