My previous attempt at humor aside, in my dateless past (during my 3-rail experimentation layout) I had both: Lionel and MTH.
I didn't really having a preference between MTH and Lionel, it was more of "which one offered what I wanted" thing. Seeing as I did not have command control, "which system" wasn't an issue.
What I remember about my MTH Rail King engines:
* Solidly built.
* Ran slower/smoother than my Postwar stuff.
* HATED the battery needed for PS1.
What I remember about my "modern" Lionel:
* The can-motor powered steam loco I had was a jack rabbit starter with the PW ZW I was using. Ran smooth and steady once rolling, though.
* I thought the "Pulmor's" in newer releases a bit off-putting on account of their tendency to slow in curves. (Remember, I'm talking circa 2000-2002 here AND I was using a PW ZW.)
* Didn't care for the need for a battery in the Lionel sound system at the time.
What I remember about my Lionel Postwar:
* LOVED the smell when running them.
* Loved their history and construction. (Talking stuff from the early 1950s, here.)
* Was "okay" with the later 50s "cheapened" stuff, but the earlier stuff was more fun for me.
Currently:
* I still have a handful of PW Lionel , including two steam engines, and an A-A set of cast frame FA's. I really enjoy them during the Christmases they have ran.
* IF I were to re-enter 3-rail, I would like do so using traditional-sized 3-rail engines/equipment running among a "sincere" scenic effort, and emphasize the fun and simplicity from that era and not wring my hands over the the downsides of 3-rail.
So there you have it: Input that is more serious and on-topic!
Andre