Most engines are going to require you to put in time to learn them, personally having worked with CryEngine and UDK, I would count them out on the basis that they are very large and complex engines that are difficult to learn and very technical (not nice for designer oriented development).

Unity is an excellent choice, once you understand the UI. Unity is very open ended in the games it can make, the only downside is things like FPS require more code to implement than in UDK, although the asset store will save your ass here as there are hundreds of scripts available. Unity also has an addon visual scripting system called Playmaker, which will help you achieve your designer oriented development.

Lastly I'd like to add another engine to the table if you really don't like Unity. Shiva3D. Its quite a nice engine, super cross platform. It uses Lua as a scripting language, which I can testify to being a wonderful and easy to learn language. Its not free for a commercial license, but it's still cheaper than Unity Pro.

Personally I would go with Unity, although I'd like to hear more thoughts.

I wanna throw Torque3d MIT out there this is free and open source you can make it do what YOU want

I wanna throw Torque3d MIT out there

Great option for a programmer, but I'd say in this case it's definitely going to fail the "designer friendly" requirement.

++unity.