Rob,
If you have the money and want a four stroke, then do it. But be forewarned, once you own a four stroke you're not likely to want a two stroke.

The primary reasons for recommending two strokes to beginners generally seem to be, "ease of operation", and "durability" (as in the ability to withstand nose in landings). But if you have a good instructor, and aren't too prone to overstepping your abilities, then I don't think either of these is a decent argunment.

A good instructor will help you set up your engine and getting it running reliably. Once that's done a four stroke rarely needs "tweaking" unless there's a drastic change in the weather. As for durability, an instructor should prevent anything that would damage a four stroke at least until you've soloed. And in my opinion, a good instructor will get you to the point where that first crash won't come until some months (at least) after you've soloed.

A 52 four stroke, as in OS, or Magnum would be fine for a 40 size trainer, as would a Thunder Tiger 54, or a Saito 56. I don't know anything about the ASP's so can't comment on them.

I too would say "stay away from MDS", or as I usually hear them referred to, "Multiple Dead Sticks".
Dennis-