The English PCP's offer great accuracy and fair power depending on the model you look at. I have to say though that my old Korean Career 707 II in .177 was THE most accurate PCP I've ever owned. I can't speak about the Sumatra though as I only owned my Sumatra for less than a month and never did any real distance shooting with it. The Chinese guns can be a bit of a crap shoot, I've owned two Chinese PCP's and one was bone stock and "ok" accurate, but I also have a pro tuned Chinese PCP and the groups are somewhere between spectacular and fantastic. My pro tuned Chinese B51 has a stock barrel, but has had the barrel lathe crowned and velocity set for a really tight fps spread, less than 25 fps in a 30+ shot string. The English PCP's have an excellent fit and finish, and generally don't need a bunch of work to shoot straight out of the box. The Chinese guns usually need at least a little TLC before they can reach their full potential, the Korean guns can also have some issues from the factory. Personally I think it comes down to a few things, budget, use, tinkerability(if that's even a word).
Use: If you are going to hunt, and going to hunt larger game the Korean guns are a good way to go. If you are planning to pop starlings then power isn't an issue with any of these guns for the most part. If you think you'll need quick followup shots consider a repeater, if you are mostly shooting from a bench then a single pellet tray may suit you better.....I've owned 3 repeater PCP's and now own 3 single load PCP's, just don't need a magazine full of pellets from a bench. Non-repeating PCP's generally cost a little less, if you don't need it or REALLY want it, then buying a better single shot gun may be better than buying a cheaper multi-shot gun. Also worth considering is noise, if you shoot in your small suburban backyard then most of the Korean guns are going to drive your neighbors crazy, might be better off looking at the fully shrouded Eauropean guns.
Budget: What can you afford? Figure out what you are willing to spend, select a few guns that fall into that price range and select the one that fits you best for your use. Don't forget, to realise the accuracy of many of these guns a decent scope and mounts is needed also, keep that in mind when you budget.
Tinkerability: If you're going to tear it down to the o-rings and fiddle with hammer springs, then maybe look at the Chinese guns, they will need some tinkering. You could also buy a fully tuned Chinese gun for a few $$$ more and still have a good gun at a fair price. Me personally have no inclination to tear down my beautiful Air Arms S400C just to see how it works, but tearing into a Chinese B50 wouldn't bother me at all. If I was going to buy another Chinese PCP I would definately shell out the few extra $$$ and get one that is fully tuned....I've owned both and would never buy one un-tuned again.
hth,
