Good luck with your choice, not so much on the highways and open areas but driving in the towns and villages is nothing like driving in the US. You have to relearn where the left side of your car is. Making a right hand turn from/to the left lane is tough with you brain screaming “DO NOT DO THIS!”.
Even the main drags are often barely wide enough for two cars with other cars parked halfway out into the lanes. Oncoming traffic and lorries are coming through regardless and expect you to make room. Throw in roundabouts with exit signs and lane markings to read at the same time and I had no time to worry about learning to shift with my left hand.
I have been there enough that my brain does the switch automatically but I still insist on an automatic. Actually I’m more dangerous on the back roads where there are few traffic cues my first day or so home after 2 or 3 weeks in the UK.
Your mileage may vary....
Left turns are easy in the UK. Right turns are as much a pain as a left turn in the US. The "fast" lane is the far right NOT the far left. Another adaptation. Roundabouts are much larger in the UK. There is time to think about the right way "out" to your intended destination.
I had enough trouble remembering which way to look before stepping off the kerb in London, let alone driving!