Some catering depots use the new 197 trolleys (the black ones) but there's still Arriva teal trolleys knocking around too.
Speaking to the hosts they find it easier leaving the trolley somewhere with more space as the 197 aisles are quite narrow - particularly if you've got people sitting side by side with their elbows in the aisle. They often walk through offering refreshments then go to the trolley to get the order.
I prefer to sit in the section near the cabs (front or rear - no real preference although I do like standard plus!) and the catering staff will generally just pop their head down from the door area and ask if anyone wants anything for these small sections, which makes complete sense. They’ve usually walked through the rest of the train from what I can ascertain though.