Thanks for all the infos!
Finally found a list with the differences The different MachineDrums? - #8 by AdamJay
MD MK1 (2001). 32 steps, thicker case, noisier jacks, MK1-only PSU. Cannot sample.
MD MK1 UW (2005) 32 steps, thicker case, noisier jacks, MK1-only PSU. CAN SAMPLE.
MD MK2 (2007) 64 steps, thinner case, less noise. Cannot sample.
MD MK2 UW (2007) 64 steps, thinner case, less noise. CAN SAMPLE.
MD MK2 UW+ (2010) 64 steps, thinner case, less noise. CAN SAMPLE and store multiple “Slots” (projects) and store multiple sample banks.
I’m 99% sure I’ll never use samples and resampling and all that, so I guess an MD MK2 [without UW] but with +Drive upgrade is what I’m looking for …
(edited: UW not UK 
)