yeah, how you hold the mouse might affect your decision. All it comes down to is if you rest your palm on the mouse or only use your fingers to move it around.
G9/G9x includes interchangeable grips for both styles. I have the G9 and liked it a lot, but eventually replaced it for the wireless G700 for my desktop; gonna bring it out again for my laptop because it's a small mouse. Software lets you keep multiple profiles to switch between with a button on the bottom. You can remap every button to a keyboard command (true for all logitech mice) and almost play Diablo 3 with one hand.
G400 is actually an updated MX518. I never read up on the exact difference, but the MX518 is one of the top gaming mice. It's only dated if you care about onboard memory or higher DPI or adjustable weights.
G700 is what I use. For the expensive price it's wireless (or wired if you plug it in), has tons of buttons, and comfortable to use.
I briefly used the G500, which is almost like the G9 in an MX518 shell. Can't say more on it. Tried the Razer Naga Hex and didn't like it. That had 6 side buttons, instead of the normal Naga's numberpad amount, but all those years of Logitech condition made it feel off to me.
Currently using the CM Storm Spawn....perfect for claw grip. So is the G9X.
(Image removed from quote.)
G9X is the second from left. Storm Spawn is the ugly bastard in red.
That second from is the Roccat something or other, right? I remember reading good things about it as an upgrade for the MX518.
oh, and Roccat has a new mouse with achievements. No joke:
