I don't think the views of the Lake are as good at Harrahs, but if that's not important to you, then I think the rooms are bigger and nicer than Harveys.
Last time we stayed at Harveys, it was mid-week, and they had booked us into a suite (I didn't ask for a suite, but I am higher diamond) at the end of the hotel, with a balcony, facing lake Tahoe. It was a huge "true" suite (separate bed/living area) and the bathroom had a 2 person jacuzzi tub and steam shower. Probably the most awesome room I'd ever had because the views were incredible. The sunrise and sunsets were breathtaking.
I'm not a fan of either casino and never seem to have any luck there.