We prefer the Palazzo to the Venetian. Its a bit more staid, and upscale, and the clientele seems to be a bit more refined. The casino isn't as crowded as the venetian, and it just seems to have a better, more classic "feel" to it. Great restaurants, and promotions as well.
The rooms are just like the Venetian, just newer (on the whole).
One of our favorite places to stay in Vegas. Great location on the strip, as well. Huge pool(s). Great people watching.
Of late the promotions have really scaled back... Vegas must not be hurting anymore!