I've been to Morton's in Vegas a few times. Each time, my steak had to go back one or more times. This particular Morton's seems to be inconsistent with the rest of the chain.
Been to the Vegas location of Ruth's Chris several times, too. Have yet to be disappointed there. Everything was prepared as ordered each time.
I have to second the Prime recommendation. ^ I have eaten at many of the premier steakhouses in Vegas, yet this one stands out as my most perfect dining experience. In fact, I have a booking there next week.
If you choose Prime, it's never too early to make a reservation. Sometimes, without advance notice, it's difficult to get a table even if you're a Bellagio guest.
At totally the other end of the spectrum, for the best pizza in Vegas visit the Metro Pizza on Tropicana. (Other locations may have been sold and still use the name, but this one is the one you want!)