There are so many tracks to choose from.
The ST 100# track is nice, but I find it's good in limited quantities and really good for specific places like the ballast-less track is great for sidings and those old branches which had nothing under them. The black ballast and rusty track too is good for coal mines and places like that. The staggered ties are perfect for the less than well maintained branches and sidings, however, I find overall that the segment lengths on this otherwise really great track repeat oddly so that ties don't spread out evenly when there's a large amount of switches such as in a yard. The track is also a bit high poly too with some very obvious LOD breaks. I hope this doesn't sound harsh on poor Adam who made it. But nonetheless, I do use it as I said in limited quantities.
For mainline track, there's JR track such as their various ones now supplied with T:ANE and if you get their Legends of the BNSF, there's a nice selection of new track with that, and as a freeware pack from their website
www.jointedrail.com.
On the DLS there's SAM-series track. This is actually European, however, there's some that has no screw bolts so it looks like it's been spiked to the ties rather than screwed down. The track is also has fairly low poly-count so there's little performance hit, and there's a nice selection of shiny and rusty track with the same ballast, which I think is important. The track also blends with other spline track such as the ST track mentioned above if you want to use that for sidings.
Then there's the procedural track. There's a new selection of NSWGWR track. It's Australian, but unlike the UK track which came out first, this looks very American. My complaint with it is the ties are still too sparse and thin compared to our track, but then again that might be the choice for the pro-track anyway no matter what so we're stuck with it. There are variants of this with very rusty, somewhat shiny, set on cinders, has ballast, etc. With the pro-track, you need to watch your track angles otherwise odd things happen with junctions, which either do not form or have missing ties.
My track of choice at the moment is Jointed Rail's BNSF mainline, and variants for sidings along with their NS 4 and NS 5 track, which came from a route I installed from them.
What to avoid...
Don't even look at the old ca. build 2.0 track. It's really, really horrid and does not look good. It uses what's called a chunky mesh and is clumsy with its printed on textures and rails. Avoid the MARTA and MBTA track from the DLS. The texturing is nice, but there's little LOD so this track in particular will cause your machine to stall.
As far as being prototypical? Well that can be difficult. The 100# rail is close to what was common in the US at the time, except for perhaps the NYC and PRR which used 120# rail for their mainlines. The 100# rail is a close match for the 85 which is/was common for sidings. What's interesting is the old Boston and Maine did not ballast their mainlines until post WWII. Instead they used old cinders from their steam locomotives. The cinders didn't even bury the ties so the track looks unballasted in many places, and I'm sure many branches and sidings probably had little if any ballast such as their shortline connection Hoosac Tunnel and Wilmington (Hold Tight and Worry), which used no ballast at all.
In the end, it's your choice, though difficult to make. I hate to say how many track splines I have gone through. What was my track of choice one year, changed many times over the course of more than a decade of using Trainz.
