I tend to like tough Democratic ads, especially if they deliver the shiv with a gentle touch. I think this Joe Sestack ad (PA-Sen) hits the spot:
… but will voters agree, or will some be offended?
On the other hand, I suspect this Jack Conway ad (KY-Sen) will work for it intended audience, although it doesn't work as well for me:
Conversely, this Solomon Ortiz ad (TX-) has a good concept, but I don't think the execution is all it could be (especially as it stomps on the last point, which suggests the opponent could be a big target):