I think you might receive more useful answers if you specify a price range. Originals in working condition can easily run more than ten thousand dollars for a restored State set. An original in great condition went for a quarter of a million dollars a few years back.
The same State set in Lionel Classics reproductions (contracted by Lionel in the late 1980s through Mike Wolf before he went his own way) could cost a tenth of that (around $1000 to $2000 in like new condition). MTH branded stuff might be a bit less because of the non-Lionel nameplates, but might be pristine compared with originals. If you want something less gigantic and expensive than a State set, you can find some smaller standard gauge locos and cars for a few hundred dollars, either prewar in beat up shape, or MTH repros like new from recent decades. If you are not concerned with brand, there are various repros or originals over the years by Williams, McCoy, etc. that might be functional and less expensive out there.