They're ALL evil, they take time away from subsimming!
Seriously, depends on what you want in a train simulator, the most realistic LOOKING one today is Railworks, but it currently has operational flaws in the AI traffic trains. This guy here;
http://forums.flightsim.com/vbts/sho...0&postcount=13
Sums up the good points and bad points of each pretty well, what he says about railsim applies to railworks since that's the current version. Playable demos of two different types;
http://downloads.gamezone.com/demos/d3254.htm
http://www.bigdownload.com/games/rai...imulator-demo/
Will give you a feel for what each of the two present day competitors run like.