IMO, it really depends. I don't think there's one area in the UK that has the "best" healthcare. At my GP surgery, there are some doctors I love and think are amazing, and some I really try and avoid as I don't think they're nearly as understanding or helpful.
In a city (ex. London), I've found that the waiting time for non-urgent GP appointments is on the lengthier side (approximately 2 weeks) due to the vast amount of people who need access. In contrast, in more rural areas, I've gotten a non-urgent GP appointment within a few days of calling.
On the flip side, if you live in more rural areas, access to specialist services may be more difficult as you will likely need to travel a bit to get to a hospital, and due to travel practicality, you may only have limited options of which hospitals to choose from. In a city; however, there are usually quite a few choices and relatively close to you.
IMO, it's similar to the US. In any given area, you'll have good and bad doctors, and good and bad services. Rural areas may pose challenges urban areas do not, and vice versa.