All armor tank companies.

Is it just a local thing? Because from what I have read it sounds like Infantry have been dominating the tourny scene on the international/national level. Keep hearing how overpowered British infantry lists are and have been placing heavily and high in the tournaments. Another trend that has been obvious is that.... well Americans suck. They seem to always do badly..doesn't mean they can't win, but at tournies they usually fair badly so they are not very competitive. The power levels of armies though really are based on balance issues with army lists and specific army rules, not with the games rules itself. Soviets have become very powerful in large part because they have gotten a shit ton of content dedicated mostly towards them with late war. Soviet tank companies I would imagine being popular due to them having such great variety and power for cost, while I bet a large factor against infantry soviet lists is.... well lot of people are probably turned off by the idea of painting a gazillion soviet infantry figs.

As for power gaming, despite what people like to think, it exists in pretty much every game, just some games are more obvious than others. Flames of War has the benefit of crazy large amount of army lists and build variations a person is capable of, in games with higher build restriction to army lists and less variety, the power levels will always become more apparent.

In some games certain builds/armies have an advantage over other armies, but they aren't unbeatable, while in some other games certain armies come off as just broken and unstoppable. A major factor also is how the matches are done in particular games. In 40k for example tournies often use the same standard missions which make it easy to build uber lists around, while other games have more objective and variable scenarios that mix things up, and help alleviates the planned cheese list as a person has to plan for everything.

If you hadn't read it, this was one of the more recent 2010 nationals results break down that does a good job breaking things down: http://www.belloflostsouls.net/2010/07/flames-of-war-nationals-2010-where.html

Yea not one US list in the top 20 even.

I think lot of people like the simplicity of tank lists. They can be fairly versatile and it's just easier to play than infantry, as well as easier to build and paint vehicles. Tank companies seem to be what most people who get into the game like to gravitate to at first because of how much simpler it all is to put together a quick army... and it won't totally suck.