The larger packages may save you a little money up front, however if you ever decide you would like to use something you don't have in your original package the track libraries can be purchased separately and added later.
I forget which package I started with, but I thought it would be all I would ever need. It wasn't too long before I was adding another library or two here and there. I started out using Fastrack and Realtrax and have now ended up using Atlas track and switches which I now plan to stick with, I really like the Atlas track system.
As StPaul said above, calling might be your best bet and they could help you with your selections and maybe save you a little money in the process.
They also have some libraries of sample layouts in a few different track systems which might be nice for someone just starting out (as I was also doing a few years ago). They are nicely done, but unfortunately they were also all at extra cost if I remember correctly.
It's a very capable program. If you take the time to learn it well you can do some really nice track designs. I am not one of them, but there are several folks on the OGR forum that are very well versed in using it and they will help you if you need assistance.
Good luck and have fun.