urgent advice regarding where to train UK or USA?

You keep saying partner in your post. The immigration service does not recognize partners only spouses. If you are married, then you need to start the process of getting a green card as a spouse of an American. This can take time. If your aim is to work in America with your spouse then it would be better to train here. You need to talk to an immigration lawyer about the long and complicated rules of getting to America legally.

only you can decide but if you know you are looking at the US and decide to train in the UK I am sure with arrangements with uni they can make sure you get enough hours in all specialties, after all they do get international students and will need to meet their country requirements. If you go to the US then fees will be high and no guarantee you can work with student visa, if you get work permit it does have limits especially first 12 months and have to show proof of funds up front. If you train in the UK you are still looking at over 2 years before you move to the US and work (that is going through the process with no retrogression, that may take longer). If partner opposite sex you could look at marriage and may find fees in the US a bit cheaper but if same sex then have to consider student visa or training in the UK and then follow once you complete your training.