The advantages for cable are (assuming you want a DVR and HD): 1) lower up front costs because you buy nothing and, at worst, have to pay a small installation fee, and 2) more properly integrated HD locals because the HD locals will just be another channel on your system while, currently, you must use an external antenna for HD locals with DirecTV's HD DVR (it is currently the Tivo, but that will likely change within a year).
The advantages of going with DirecTV: 1) lower price (unless you're buying every premium channel, in which case, cable channels may charge less per channel); 2) NFL Sunday Ticket (available nowhere else); 3) Tivo (the Tivo HD DVR is, hands down, better than any other HD DVR, but when DirecTV starts broadcasting new HD channels using MPEG-4, you'll need to move to their DVR, when available, to get those channels negating this advantage).
I've had DirecTV in HD since the days when the only channel you could count on having any HD content was the demo channel (with Dennis Miller in HD despite his show being in SD), and the only actual HD channel being carried was HBO. I've heard people claim about limited bandwidth on DirecTV, and I don't question their accuracy, but I do question whether or not it reduces my enjoyment of the channels. I've always been quite happy with the picture.
And I've heard people mention the rain fade that can happen with satellite. This is true, but it's also uncommon. For me, it has to be a fairly strong rainfall to see any problems.