I've tried the mouse and cursor, and I've tried on my Wacom 21UX, which is a large touchscreen designed for stylus use. I prefer key and mouse!
There's just a little hitch in the timing when you grab a tile, not to mention the stop in time when the tiles cascade. With the cursor, it's a little easier to know when you've actually grabbed a tile versus hovering over it, or when the tile is automatically ungrabbed during a cascade. With the touchscreen, this feels ambiguous to me. I wish the tiles could change a little to let you see which one you've grabbed or ungrabbed, the same way the tiles highlight when you are close enough to a match.
The other big downside to touchscreen is that my arm blocks the view of the lower tiles when I am moving things. I love my carbs too much to go anorexic just to see more tiles under my arm.