For me, TC got it right with the Plethora pedal. I can have multiple effect boards each comprising of three effect slots (mine is the x3 which fits neatly on my board, and there is the bigger x5 if you need more slots). As many have noted the biggest drawback is the lack of a good bass overdrive or distortion but for me my always on SansAmp takes care of that. There is no preamp either (it is just a multi fx) but for my needs it is more that sufficient.
For me, the key to any multi fx is the ease of use, both in terms of setup and use. I don’t want to learn a programming language or remember a list of foot tap sequences to access a good compressor, a bit of tasteful chorus, and a little bit of octave action.