I agree that you probably shouldn't go to a server in the last bracket of the WvW ranking, as the last tier is really screwed because on both the European and the NA side there is only one server playing against probably 10 people from the other two servers spread over all four maps (from the looks of the scoreboard at least

).
But other than that I disagree with the notion that you have to go to T1/2 to get decent WvW action.
I am on Abaddon's Mouth, a German language Server that has never been higher than rank 12 but also never lower than rank 20. So, we were pretty constant, despite some servers plummeting from the top tiers due to drain of players jumping another bandwagon and other servers rising like shooting stars because they were the target destination of the previously mentioned player movement. (Therefore, I applaud ANet on the decision to finally shut down the server transfers! It should have happened a lot earlier, though!)
Despite not being a high ranking server we have some serious WvW action going on. It might not be as constant as on the higher servers (mornings and nights the server-TS is pretty empty most of the time and so are the maps), but to me this is not really a downside. You don't have such long queues (normally during prime time only EB and maybe the own BLs are full, so there is always room if you're willing to start something on one of the opponents BLs) and there aren't such massive zergs. We only get more than 50 player zergs during organised events that have been adverdised by the commander for some days prior. Normal public zergs are rather around 30 players and there is plenty of fun to be had for smaller groups, too.
So I think, unless you want to get bragging rights for being on the top server of your continent, it's even better to get a server in the middle of the ranking as you will have no problems to get on the servers and you'll still be able to find enough action.