
If you choose one of the above, you're going to need some new vehicle sets as well, as default OpenTTD vehicles don't always provide support.

They introduce new cargoes and industries and also alter how the economies work. ECS Vectors and FIRS mostly dominate this, but you have some variations of the default industries such as Pikkabird's PBI/UK Industries, McZepple's Manpower Industries, or YETI. Typically the big game-changing NewGRFs are industry/economy NewGRFs. Before adding something, take the time to read about it, learn about it, see what others say about it and what issues they encounter. That doesn't mean you can't get in over your head. OpenTTD itself is regularly maintained and improved, occasionally adding new features, so there's nothing that a script or a NewGRF fixes. There's no "best" because all of them are essentially variations on an already excellent game. That's also pretty much the same situation with scripts and NewGRFs. You'll have to find the discussion for each AI on TT-F and read about it and decide if it's one you want to play against. There really is no "best" one, as AIs are typically created to suit the interests of their developers.


Many of them have esoteric bugs that have never been fixed. Basically a lot of them still work just fine and their authors have felt no need to add new features. As was pointed out, there is a discussion topic on TT-Forums about which ones are or are not updated, still maintained, etc.
