In summary:

Oman has more than 5* hotels, shopping malls and a few reconstructed forts. While Yemen is at war and Saudi remains inaccessible for tourists, it's the only Gulf country where you can see any local culture and natural beauty (other than sand dunes). It's also still relatively easy to visit, not super conservative and has material comforts if you're into that. Until Yemen is rebuilt, it's the best place to visit down there.