This is a very informal description of the scenario described in the default.config shipped with xtrek.
Klingon : heavy phasers, low torps. normal engines, but they can't slow down very fast, so turning is slower than normal. low fuel gain-back, but they make up for that by toasting anything that gets near with the phasers. best cloaking costwise ...
Romulan : nickname 'garbage scow', pretty accurate. slowest turn rate in the game. heavy torps that will rail an opponent that gets caught in a stream. best shields, and in terms of how much energy they chew, best cloaking since they also have the best energy regen rate. hull strength also highest.
Orion : tend to spit torps, which are generally weak but very cheap and fast to fire. best acel/decel in the game, and turn on a dime. hull pts and shield are the lowest, so they need those engines of theirs often. regen is also low, so they need accuracy on those torp shots. phasers are also weak, and don't have a very good range. mostly useful for annoyance shots and close in fighting.
Federation : this is basically the standard xtrek ship of old (we had to keep one of them around :-). All around average ship. High cloak cost, but also have a decent regen rate. Best repair rate (Scotty factor), and their weapons are both pretty potent. Can get out-paced if they don't watch out, though - especially by Orions.