So that none mistake me for a Festool DOMINO shill, I'll
pass on some of the previous responses.
To the question - with a barrel grip - your pushing hand
is more in line with the cut to be made than with a D
handle, so you're less apt to rock the tool - and make a
slant cut - or a sloppy one. The size and location of the
the fence handle is also important. You want the hand
on that one to be pushing DOWN, not down and foreward.
The Porter Cable with the big U handle on top encourages
rocking the tool - a dumb design idea. Handy to carry the
tool around - but dumb when actually using it.
Just something to consider.