What English dialect (US or UK) do you use, and does it matter which one you use?

I use UK English as I was born and live in the UK. Both are very similar as they are mild variations on the same language so talking to people fromt the opposite one is not a problem.

Not all English is just simply English. As we all know there are different varients. In America, we usually greet someone by saying, "Hello" or "Good Morning". I think England is the same in that regard, but go to Australia; they greet people by saying, "G'day Mate".

I do realize that you're asking about US and UK. Pretty much, there's not much difference between us two, but if you go to other English speaking lands, you will find that some words don't exactly go too smoothly. If I'm correct a napkin in Australian English means diaper. Try asking for a napkin the next time you go to Australia!

"UK English" is mostly regarded as proper English, as England is where it orginated from and is standardised through the Oxford English Dictionary. I have been informed from a few sources that America does not have such a national standardisation, though I may be wrong.

"US English" is wider known as it is used in most businesses across the globe due to America's influence. It is sometimes seen as a 'dumbed-down' variant as letters and words have been dropped from "UK English". However "UK English" is much more diverse and constantly changing at an overwhelming rate, this makes it a very hard language to learn in comparison to it's American counterpart.

I would say that if you live in the UK, or spend a significant amount of time there, you should learn the "local lingo" per se. If you live anywhere else or are trying to learn English, learn "US English" as you will be understood almost wherever you go.