D Grip vs Barrel Grip Jigsaws
Its personal preference. Couple things to note:


With the top grip saw, its more
natural for me. I look down on the
cut, where as with a barrel grip I am
looking to one side.
The switch placement on a top grip saw is more natural for me as well.  It is usually a trigger under my index finger.  A barrel grip has switch placement on one side.  
Top grip are more wrist action saws so they can be easier (I think) to do more scroll work. 


It is mostly personal preference though. I would try would a couple saws.  However, I would bet you would be happy with either.