Mature, mostly because extra mature is frequently drier and flaky, so annoying to grate if I'm using it to cook. But if we can afford it, Czerwiks sell a damn fine chedder that's been smoked using applewood, it's gorgeous and not too pricy, so we buy that when possible.
Yes, I am very partial to applewood-smoked cheese.
It is very hard finding a good mature cheddar here in the US without paying the moon.
Where are you living these days? I can find decent and not-insanely-expensive (still kinda expensive, but not ridiculously so) mature cheddars all over the place here in the hippiest part of California.
Phoenix, well Scottsdale to be precise. It's always that balance between quality, convenience, price, laziness. I mean I have actually found pretty good cheddar in Costco of all places but then it becomes a trip to Costco rather than just popping round the corner to the grocery which is foo foo and overpriced but round the corner.
There's more to it than just maturity. Old cheddars can vary wildly - some just get one-dimensionally sharp, which some people love, but these people are idiots because that is no good at all, while some develop rich and complex flavours. I like those ones.
For a long time my local supermarket (part of a large chain) had a bulk cheddar that varied from edible most of the time to a richly flavoured, sharp cheddar fit for gods to fight over. Then the chain was sold and the cheese changed. Now the quality is far more consistent, but it's consistently bland and edible now. A sad day.