The UK "Championship" system was specifically designed to promote the better players rather than the most powerfull lists. It is also worth noting that other people are less successful when playing with exactly the same lists as those who win the tournaments, showing that skill and regular games / experience are key (as in any competition environment).
Some lists are definitely more popular than others, suggesting that these are possibly slightly more powerfull, though I believe the presence or lack of models also plays a significant part in the player's choice of list. However it is also worth noting that there are definite themes in most armies (often to match the perceived 'fluff' for the particular army / list) and their interaction with the E:A game mechanics can benefit or hinder the list.
I am really unsure whether this makes one or other list 'better', not least because it is almost impossible to measure the quality of E:A lists produced by the various communities. The main question is rather whether you enjoy playing the E:A rules, and more importantly whether you enjoy playing with your opponent enough to want to repeat the experience. This "enjoyment factor" encompasses so much more than the list in question. . . . Which is why the golden rule is DWWFY
