I love my 6" Festool, greatest piece of equipment I have bought so far for the shop, and it's full of tools.
Being able to switch to the rotory mode, it can sand/grind/cut anything, quickly, level and clean. I run my to the shop vac and there is no dust, sometimes chips/chunks, but no dust. In the randam mode, it beats any other sander I have own. Recently had six maple raise panels to sand. I hate working with maple as you always end up with sanding marks once you stain. This time I had none.
It isn't cheap at $440, plus it uses it's own sand paper, so figure another hundred for a good assortment of paper, but it's worth it. I am giving serious thought to picking up their router, based soley on how well the sander takes care of the dust.
Back to your question, I won't buy a 5" sander. Too small for my projects. I like I have said before Rigid makes a nice 6" sander, dual mode, 1/8 and 1/4. Hooks up securely to the vac and I believe they worked our their switch issues.
I am not a big fan the of the dewalt sanders. Didn't seem to have enough power and left alot of swirl marks, you have to move it very slowly.
If you interested, I would sell my old 6" metabo sander. Works good, doesn't have a whole lot of time on it and it in pretty good shap (now that it's fixed). Shoot me a pm if your interested.