I don't want to turn this into a political thread, but think about the future and the likelihood of the bike being off the road whilst repair work is being done. Whilst we all like to think that our bikes will go on and on without fault, it's a sad fact that they are not always that reliable. You just have to search the threads on this forum to discover that.
Most Bafangs are easy to fix, with parts being fairly cheap from China and expedited delivery available. Parts are always in abundance and you should have no problem sourcing them.
Onto the Bosch, now that might be a different situation. As vfr400 states, they usually aren't fixable by the owner, requiring you to go through the Bosch system for repairs. What with the potential for a no deal brexit coming up, this might exacerbate the repair system, with parts being in short supply and long waiting times.
I might be wrong though, and this is only my personal opinion. Just to put this in context, my Bafang mid drive has had a few issues here and there, but have always been repaired by myself fairly quickly. I've managed to source parts from both the UK and China pretty quickly. Knowledge on Bafang systems is more abundant than the Bosch, but yet again, this is only my own opinion.
I'm getting the vibes that you are after a ready built bike, but if you are handy with a basic toolkit, then a Bafang BBS01 would be the way to go.