The Rack-Version sounds the same as the lunchbox. However, it has two knobs less (for modulation), has the USB-Port on the Front and doesn't have the LED-Collars around the Bass, Middle, Treble, Presence and Volume Knobs.
This made me choose the Lunchbox-Version.
The internal Poweramp is solid-state, so it does not color the sound. Using a tube poweramp or the fx return of your amp would result in having two tube poweramps (the simulated one and the real one). This would have an impact on the sound (not necessarily in a bad way though).
If you would want to have an external power-amp you could use something like the Matrix-Poweramps or an aftermarket amp that fits in the back-cavity of the lunchbox (ambrosi, etc.)
I went for the powerhead, because that gives me more options, doesn't weight much more doesn't need more space than the unpowered version.
I'm using it with my 1x12 vintage 30 loaded cabinet. It has 16 ohm and can take up to 60 Watt. I didn't have problems with that combination at rehearsal or gig volume.
I went for the Behringer with Uno4Kemper-Chip 'cause the Remote is pretty expensive and you need to buy external expression-pedals.
Funktion-wise the remote can do a bit more (looper, easy assignment of funktions) but lacks the abbility to be connected to other gear.
So if you are willing to spend more, don't want to program your controller, need a looper or want to use specific expression pedals, you should go for the remote.
I just needed to change performance-slots and switch on/off some effects. Also the two built-in expression bedals of the fcb1010 suit me just fine.
I don't have the fcb1010 for a long time though, so i can't comment on reliability.
I hope that helps