Jennifer's question was answered many posts ago, but this has been an interesting read none the less. And to some degree shows what I have always said, that this small O gauge market place is a very diversified one indeed.
Some people will never overcome their opinion of MPC as "mostly plastic crap." Well, from reading here on the forum, one could just as easily make a point that the current stuff is mostly electronic crap: failed circuit boards, blown master boards, faulty smoke units, etc. And with the LOW production runs of these products, you can rest assured that specific parts will not be available in the future, as they STILL are for MPC products 40 years later.
MPC may not be everyone's taste, but the stuff is in most cases a bargain price when compared to new stuff. Parts are readily available and will continue to be as their is the demand enough to justify them. And if you find something where you can't find parts, the trains were made in quantity and are affordable enough that you could purchase another unit to cob for parts.
Even among MPC fans, you find the opinion that the beginner DC stuff was Lionel biggest mistake. WHY? They were low cost sets to introduce new comers to the hobby. Most likely someone buying one of these sets, wasn't going immediately expand to a Hudson or a GG1. And it's not hard at all to wire up both a DC power pack and a Lionel AC transformer to the track, so you can run both.
And plastic wheels... easily replaced should you choose. I buy the Lionel or MTH wheel cars and exchange the metal wheels on the flat car with the plastic wheels that come on some of the short 027 MPC cars. The plastic snap rivets used to hold the trucks - also easily fixed.
I happen to really like the Lionel Industrial Switcher and I jump on them. They're easily repainted, kitbashed and improved. I run my layout on DC current, so I have extra room inside these for added weight, so they easily pull a 10-15 car train. I've added headlights to all, ditch lights to some, strobe lights to some, added handrails, etc. Since I took this picture, I've added front and read handrails to the engine.
The flat car behind the engine, is a repainted short 027 MPC flat with added warning signs along the sides, repainted K-Line gondola LCL crates with flashing lights wired into the red plastic beacon on the top - and thus I have a shorter length toxic waste car completely unique to my layout (along with the engine).
I'm in this hobby for fun and to not break the budget... MPC products fit the bill for me. I'd rather have fun with the trains than complain about them. If something isn't made, I'll take the challenge and make it myself... that for me, is what a hobby is about.