Welcome to FlyerTalk.

Many airlines are moving to revenue based programs. Accumulating miles is becoming less attractive. If I were you, I'd first start with finding out the carriers on the route and the prices for the tickets. If I had solid choices, I'd look at the mileage programs next.

I like looking at flights on flights.google.com. Plug in Manchester/Nashville. We often talk airport code around here. Your codes are MAN/BNA. Then look at elapsed time for the total trip and the number of flight segments. It would be great if you could do the trip with just 2 segments. That's tricky, as Manchester doesn't have as many flights as London and Nashville isn't a major hub airport. Still, I spot a US connection via PHL. It takes 12 1/2 hours one way. US is merging with AA. AA has announced it will NOT be going to a revenue based program in 2015. This could be a good place for you to start.