I would say Natwest - as you say customer service top notch, and you shouldn't really need a huge overdraft - afterlal your going to have ot 0pay it all back at some point.
The freebies at Natwest are better!
I think Halifax is a bank...
You can use most cashpoints for free with your card, so i don't think you need bank specific ones so i don't think cashpoints are problems. Natwest has at least a one bank in most towns, not as many in scotland, but still enough. Overall i would say natweszt ahs most cashpoints at a guess though.
Its simple to move banks, go to natwest, open your account, go into HSBC demand to close your account and transfer your money across to the new account. (probably best to wait for the natwest one to be properly open first though). I think you can get your new bank to take control of the transition, but i think its best to do it yourself...
I think SLC will need at least 2 weeks notice to be safe.