just for the fun of it, I started a game where all 8 AIs currently available from the content server battled each other. And I thought I'd share the results with everyone...
The contestants:
* AdmiralAI (v19)
* CluelessPlus (v3)
* Convoy (v10)
* Medieval (v2)
* OTVI (v1.4)
* PathZilla (v5)
* PAXLink (v4)
* WrightAI (v2)
A little disclaimer: the results I got here don't necessarily need to tell the real "performance" of the AIs. It's only one map, one specific NewGRF setup, one setup of settings. Some of the AIs may perform better or worse on different maps and/or settings. And some AIs that didn't perform very well in my little game here might show some impressive results when working on their own, rather than being faced with seven opponents.
So please don't take this as a general "ranking" of the AIs we currently have here, and to the developers of the AIs that were outperformed by the others in my game, please don't be discouraged! Please keep developing, it's nice to have a diversity of AIs available

I chose a temperate randomized map of dimension 512x512, with the following NewGRFs (It's basically my standard GRF compilation, but without the 2ccSet, because that from my experience causes trouble for AIs using trains (i.e. AdmiralAI) due to their high costs.) The following posts will contain results from different stages of the game.