Unless you ride on some pretty seriously rocky trails, slicks will work better for you and won't sound like a motor cycle on the trainer.
I'm sure others will argue, but I'm not a big fan of real skinny tires on mountain bikes. I think that anything less than about 1.5" wide looks goofy. I've got 1.9" tires on my beater bike and never thought I paid a performance penalty over skinnier tires.