From the perspective of a Lionel guy, another reason to like the "old" PS1 steam engines from MTH is that you can have Gun Runner John's TMCC and a Super Chuffer installed....or do it yourself.
Lionel has never made a C&O 614....and I have one with GRJ now. The other MTH steamer that I'm after (for conversion) is the Great Northern S-2......which Lionel has not yet offered either.
Lastly, I really like the deck plate/apron that MTH offers on their steamers now. It's a nice touch, IMHO.