If you intend to play the pre-mounted NSSA game you'll find a pistol grip the consensus favorite. Next question would be what sort of PG do you favor. Most target guns seem to have fairly tightly curved (sometimes bulbous) grips. I think the idea is to place the trigger finger in a very consistent location. Older K-guns often have a very nice, almost POW, gently curved PG.
If you take the view that skeet is practice for field shooting then go with whatever grip you prefer in the field.
Vintage skeet guns - from the pre-mounted gun days - with straight grips seem to find their way into my life....and stay.
Sam