I'm your guy for logitech mice.
I've owned and used thoroughly all of the following: MX518, G5, G7, G7 revised, G9, G500
My current mouse is the G500... my brothers have my MX518 and G7. Of all the mice, this one is my absolute favorite:
That's right... the first gen G7.
I love the glossy feel, the fact that it's wireless, how it glides, the perfect weight. It has it's flaws... that being short battery life (have to change battery every 6 hours... takes about 10 seconds to do) and a number of them are defective and have issues with disconnecting from the receiver intermittently. But if you get a good working one... it's the mouse to beat, imo.
I use the G500. It's good, but not great. The cord is really a buzzkill... frictionless scroll is mostly useless... the buttons on the side aren't as useful as I thought they'd be... nor are they very comfortable to use. I don't like the texture of this mouse either. If you need high sensitivity and want customizable weight... this mouse has got the DPI you're looking for.
The MX518 is my second favorite mouse. It has 2 very ergonomic side buttons and is just very comfortable. The cord isn't as bad as the G500 either. It seems to be a flatter mouse which I like. It glides better than the G500. The G500 is basically the same shape yet somehow bulkier... needlessly so, I think.
So in order of favorite to least favorite:
G7>MX518>G7 revised>G500>G5>G9