Define resources…

There are a few games that do a plethora of splatbooks to give you new mechanics or setting material, or reference material. If we’re using that as a metric, there’s no competition: GURPS.

What do you want to play? GURPS has a book on it. I wouldn’t be surprised if there’s a sourcebook on being an accountant in the 17th Century. It will be almost scholarly in quality (well, for today, it’ll be better than scholarly), it will plug and play. You can use the material for other games and never play GURPS. (That would be my recommendation.)

If you are talking a game with online support, apps for character building, GMing, and plenty of books with rules and creatures you’ll never use. Dungeons & Dragons, 3rd or 5th edition (I’m including Pathfinder in this, so Paizo fans settle down.)