K and Q have qmk iirc layout is the primary difference K2/K2 pro have a 84 key layout, whereas Q has a volume knob. C looks like your traditional tkl layout.
Don’t spend too much from Keychron. My K2 pro’s rgb leds died after only a month of use, while I was on a trip recently and customer support has been super slow debugging the issue.
Fortunately the bluetooth and cable in still work. Here’s what it sounds like despite the leds not working