Hi! In my personal opinion, which is subject to change, I would rank these EQs thusly:
1. EQ 81
2. P60G
3. EQ 73
4. P50B
5. P50A
The Neves and APIs sound quite different to my ears and tend to complement different sources, so it's good to have at least one of each. And within each group, the more bands, the merrier -- although there are minor frequency choice variations that may make any one of these "best" in a given situation. They're all really, really good.
Don't forget about the 432 Master EQ though. One of the best EQ plugins I've heard, although you might not be able to use it for anything but actual mastering -- big CPU hog.
If you planned ahead and stocked up on half-price Gear Credits a few weeks ago, the current Group Buy is a fantastic deal. All these plugins are among the best in their class, so being able to get them for so cheap is a no-brainer.
Cheers,
Eddie