Interesting Bob. I do know a couple of detail oriented scale (2R) modelers that prefer Lionel shells. I haven't had a Key PA in my hands yet, but the Santa Fe specific details on the Lionel (after 2003) were better than the MTH PA(90's).
I still have both a Lionel PA and an MTH PA. Off the top, the number boards on the side have the correct width for 2 numbers. The MTH number boards were more generic and were wide enough to accommodate the four numbers used on D&RGW PA's.
If I have time I will do a side by side and everybody can judge for themselves. Regarding MTH, I haven't seen anything since their 90 PA, so I can't comment.