okay, from what i've heard is, this is the order of supremacy...
the best is swissol (but costs about £60 a pot!),
then comes 'proper' zymol (which costs about £40 a pot),
then comes halfords zymol (which i've just bought at £12 - haven't used yet), then autoglym (have been using 'super resin polish' followed by 'extra gloss protection' - they totaled about £15 - good shine when you use both, but a lot of hard work).
the top two are supposed to be s**t hot, but i dunno about you but i can't afford them!! i'm lookin forward to the halfords zymol, it supposed to be better than autoglym, but i'd be happy if it equaled it as it requires less work. some people reckon mequirs is quite good, but i've heard its not as good as autoglym. some people also reckon mer is good, but i'd say its okay but i hate the amount of dust it seems to produce.
its also worth noting that autoglym is a polish, where as the others are waxes. the differences being that polish takes the top layer offf the paint (kind of like a mild t-cut), where as wax is a protectant layer. if you have older paint its worthwhile using a polish followed by a wax, but on a brand new car i'd just use wax.
these are my own opinoins gathered from listening to others and seeing some of the products used. i'm sure there'll be a pro valeter on here who will be able to confirm or disagree with my views.