The main differences are bronze or white turkey - bronze are more traditional, slower growing and have a stronger flavour. They are likely to be free-range, and they are more expensive (because they take longer to raise). White grow faster, and don't have a very strong flavour. They are cheaper and more likely to have been raised in a barn, but not necessarily. You would have to look at individual supermarkets, but I would have thought most would sell both types.
Bit of trial and error I think. Had M&S for past 5 years and last 2 really underwhelming - going with market butcher this year. Incidentally, bought one off him the other week as it was a fiver (!) and needed something quickly for lunch the next day - didn't do anything with it but bung it in the oven and it was the best Turkey I've eaten in years... - could taste it , lol.
We had two turkeys last year. First one from the butchers. Absolutely delicious. Second one from Sainsbury’s on Boxing Day. £35 reduced to a few pounds and put in the freezer. We had it late January. It was awful. Dry and tasteless. It was their best range too. It was chopped up and blended into soup. We couldn’t eat it with the veg it was served with.