Each wheel is different and has it's own 'magic' about it.
I have 4 wheels (2 antique and 2 modern). Both the modern wheels are Ashford. I don't have experience with other big name wheels.
Between the Ashford Traditional (ST, SD) and the Ashford Traveler (DT, DD), I prefer the Traveler. It is more adaptable.
With the Traveler double treadle (DT), double drive (DD), I have the option of hooking up the brake band and having a single drive (SD) with scotch or irish tension.
I have multiple whorls so I can adjust my flyer/bobbin speeds to what I want to spin. There is the optional jumbo flyer kit for plying and making large, funky yarns.
Ashfords have been around for a long time. It's easy to get spare parts (even for my 70's era Traddy) Bobbins are usually interchangable.