NHS bank HCA

Every ward is very different, and it will probably vary from trust to trust. Over time, you'll also find where you like working.
Personally, as a bank HCA I hated MAU but don't mind bank shifts there qualified. I didn't mind care of the elderly wards (there's always someone who needs the loo, has been incontinent and needs cleaning up, needs feeding, needs someone sitting with them to keep them occupied and stop them falling out of bed!) Where I work there are some very busy medical wards and very busy surgical wards (my ward is a VERY busy surgical ward!) but there's also "quieter" wards both medical and surgical.

would it be harder (require more clinical skills) to work on a surgical ward?

No. The only "clinical" skills expected of you are assisting with hygiene needs, toileting, feeding, checking that people have passed urine/opened their bowels, observations (but this is trust dependent). On surgical wards you have people going to/coming back from theatre to sort out, that's why it gets busy. You don't get expected to do dressings, cannulate, take bloods etc.