From the subjective spreadsheet I created I think I would look at these vendors to meet most of the criteria (in no particular order):

• MaxMind (it appears Wikimedia already has a relationship with them)
• IPinfo
• IP2Location

I lean towards those three because they seem to (from what I can tell) offer more flexibility over how we could potentially implement the data (i.e. having our own copy of the database, etc.). If we already have a relationship with MaxMind, that seems like the obvious choice.

You should look at Spur. We are using it at the WikiProject on open proxies with very good results. I have independently verified its accuracy for many cases, and it is far superior to every option that has been mentioned in previous discussions.

It also provides some important information for proxy checking, CheckUser, etc, such as the exact VPN and proxy services present in an IP, not just a boolean flag. A US Comcast IP with a Luminati residential proxy has nothing to do with a Bangladesh CG-NAT gateway with 5 residential proxy networks present.

Thank you @MarioGom. We want to add multiple services into IP Info eventually. We are beginning with MaxMind for now and will look into Spur in the near future. It's awesome that you've validated Spur already.