Disting MK4 is a great multifunction module that does a lot more than just FX. Unfortunately the interface is not intuitive and that can be an obsticle for some people. Disting EX includes a screen and has a better UI, but the interface can still be cumbersome.
Happy Nerding FX Aid Pro would be the way to go if you just want an FX unit. It does everything well and has a clear UI
Endorphines Ghost looks like an awesome all in one multi-FX unit
Everything QuBit makes is top-notch, but for a smaller system I'd go with a module that can run different algorithms or one that can do multi-FX. If all you're looking for is FX I'd go with FX Aid Pro (or one of the smaller FX Aid) or Ghost. If you think you might want FX+Tuner+Quantizer+SamplePlayer+CoffeeMaker then go with one of the Disting
-EDIT: Take a look at Noise Engineering Versio platform. These can load different FX firmwares