The AT-ST can be done to-scale completely without any problem, so I'm more in favor of it... The AT-AT actually isn't really all that important when you think about it. There's little interaction with characters in the movie, especially "heroes", and ultimately I think that's a factor. The AT-ST at least gets a lot more screentime.
Personally though I'm biased too... The AT-AT is simply too large to ever be done full sized, and while it could be improved, it never would be something I'd ultimately appreciate.
I don't look at the AT-ST as "a big item of the future", as AT-ST's are small, but I surely support the AT-ST getting made over the AT-AT at this point. AT-ST's simply would be doable to-scale no problem, and that gets my attention immediately.