I'm about your size, also looking for a new board, and also live in MI. I've been leaning towards the MTX boards as well because most of my riding is on ice. A 152 might be okay if you just use it as your park board, but if you ever decide to take it in powder you will not be happy. I personally wouldn't go smaller than a 155, but I don't do a ton of park riding and I'm comfortable on my 155. But as I get older and gain more wieight it starts to feel smaller and smaller. I'm leaning towards the GNU Rider's Choice 157.5.
But sorry, but I've never ridden anything smaller than a 155. I'd rather buy a board I can take pretty much anywhere. Why do you want to go smaller? I'd think your 155 would be a good park size.