Nomorehelos - I know what you mean, on our last holiday in the USA we stopped for a coffee before crossing Death Valley and I asked for a Mocha (pronouncing it mocker) - the lady behind the counter looked absolutely blank and after a couple more tries I pronounced it mowker and she instantly understood
"Mowker"? I'm surprised that worked at all, since the US pronunciation is "moe-k-uh", long O, very soft A, emphasis on the first syllable.
I deal with a fair number of UK and AUS folks. The UK accent is easier for me to understand most of the time, neither is very difficult unless it is very noisy. I don't hear too many Irish accents, but not too tough. Scottish is tough, and the NZ accent to me is nearly incomprehensible.