It's not a regional difference. When speaking carefully people say "quess-chun", but in more relaxed speech the "ch" sound often influences the "s" and makes it sound like "sh" - it's easier to say because your tongue has fewer manoeuvres to do, "sh" and "ch" are pronounced with the tongue in the same position. You can pronounce it whichever way you like, most native speakers probably won't even notice whether you're using "s" or "sh".

I agree with Coligno about this. This isn't a regional difference, and is unrelated to accent. This has nothing to do with where the speaker comes from in Britain, or even whether they speak British or American difference. We all pronounce this word in pretty well the same way, regardless of the accent we have. If you check the phonemic transcription in a dictionary, you'll see that there is only one version. It's simply that, in relaxed speech, the quality of the phonemes in consonant clusters may change slightly, depending on how the surrounding consonants are articulated. This may produce some slight differences from person to person. I pronounce 'question' like this : /'kwes.dʒən/

The two are correct. The pronunciation, depends of the region of the speaker. In my opinion, i think that you should choose which is easier for you...... I hope this can help you.....

You answered the question yourself :) It differs from every region and both are acceptable to use

The way I pronounce 'question' is probably more similar to your first pronunciation. But there is a huge amount of variation in accents within the UK, and not one standard accent found everywhere within the country.