I've tried both of these, but I'm not a big gamer. MSTS is old but has a huge following and there are a lot of routes, in fact people are still developing them for the original version (there doesn't seem to be a newer one except for patches). To create a route, the interface is very primitive and hard to work with. For routes, there are quite a few out there from various sources, but consist creation can be a nightmare if you don't have all the dependencies and you don't quickly get savvy on how to edit files (even text files) by hand.
Auran is nice, but it's a pay app, and the newest version require a fast computer to even run.
There are a few others out there, like BVE (Boso Valley Express), which is also old (from Japan) but more technical in operation. That one, in particular, offers a lot of NYC subway routes, particularly from a free Scandinavian server. It's still in use but now there is also an open source "free BVE", but not quite as mature.
Just for relaxing, though, I stick with MSTS, and once putting together successfully a consist you like, it will run on any route, and there are quite a few nice fun routes to explore. I remember a good on for the L&HR from PA to Campbell Hall as well as one for the Erie (Pt Jervis area down to near Suffern) among the ones I've tried.