If you want a Mervin board that rocks the park and is fun all mountain check out the Lib Tech Burtner BoxScratcher. I rode with a guy who was on one last year he had no issues anywhere on the mountain. Lib tried to make a park board that is an all mountain board with the Boxscratcher.
My son (115lbs size 9 boot) rides back country on a 147 Skatebanana and loves it. He is getting a 142 Boxscratcher this year as a stiffer, shorter version of his Skate Banana and we will see how he likes it. He wants a shorter board for park/spin tricks but the Burtner might be on the stiff side for what he likes and his weight.
The Attack Banana might be a good one to look into as well. It's a stiffer Skatebanana but my understanding is that it wasn't designed to be run as short as the Boxscratcher is.
Link to a quick Boxscratcher review.