People in all four of those countries love French fries, but prefer them with different condiments. Just as a refresher, the French love their frites avec moutard; Americans tend to prefer ketchup; the Belgians favor mayo, and the Brits go for vinegar, usually the malted variety.
My take is that I love the traditional American condiment ketchup, but equally adore vinegar on my fries. Recently, I was goaded into trying mayo on my fries, and I must say, the Belgians are on to something. Have not yet tried mustard on fries, but will doubtless give it a go eventually.
Do you lot prefer one of the above, or do you tend to mix it up?