I really don't see what everyone saw in Summer Sanders. I thought she did a crappy job with Figure It Out. In response to the contestant's talent, <fake enthusiasm> "Wow, that's sooooo cool!" </fake enthusiasm> Also, her hosting abilities were below par, IMO. Not the worst, but nowhere near the best.
Obviously, the best is Marc Summers. During the Super Sloppy era (maybe during regular DD), he'd sometimes make a reference to other game show hosts, so it seemed to me that he had took a little bit of their styles and mixed it with his own. The result, an excellent game show host for an excellent show. Mike O'Malley comes in second.
The worst, hands down, Robb Edward Morris. He acted like he just woke up right before taping, no type of energy at all, and seemed lost the entire time. If not for the cue cards, God only knows how he would've handled Make the Grade.