The thing that gets overlooked one versus the other is how do you store your gear. If you need your gear to remain cleaner and drier then a shell with a rack is probably going to accomplish that better. If you don't mind the dust and water having a bit more access to your stuff, or like to travel much lighter, then a bed rack is probably the way to go. In the end it's all personal preference as either way can accomplish goals, it's more just how you plan to use your stuff.
That said I went with a shell. I seem to be becoming the minority more and more. Nothing wrong with all the options out there, jut the shell works for me, especially day to day. I'm pretty happy with how it worked out.
For an RTT, go with the RCI bed rack—better weight support, lower center of gravity, and easier access. The Prinsu roof rack is great for lighter gear but not ideal for regular RTT use. Bed rack first if you're planning to camp soon.