Well here's my WWI summary for MP 1 v. 1 games:
Germany - Unless you are an exceptionally talented player with fantastic micro, you will lose to anyone who is equally good unless they don't attack you at all in the first 7-10 mins.
France - Very versatile. For a fast player who likes attacking early, probably the best civ. Attack at 3:30, self-heal, add a proxy barracks, add armory, airport/siege factory and it's game over against anyone excpet a superior opponent.
Russia - Extremely easy to play when you learn the fast AC start. Pump out a few Conscripts, then go full AC at 6-7 mins. and attack. If you have decent micro you can overwhelm most opponents by the 15 min. mark. As long as you keep your econ growing through this, you'll be able to easily add an Armory, Airport, etc. to meet any counterthreats. Just too easy.
US - Potentially a very powerful option, but you have to be smart and good against a good France or Russian player. You can mass Doughboys really quickly, and they can be devastating. But late game, you have no AA cover unless you want to micro those expensive and rather weak fighters. The key is getting a great start and pumping out DBs and Ambulances. You can overwhelm anyone who is a lesser player quite easily.
UK - What can I say? UK in Empires is a very tough choice when you play 1 v. 1 in a competitive game. Your econ is going to suck worse than Germany's early on, and you can't rush build anything because of the autobuild feature (which was probably a mistake not to allow, IMO). You have powerful units, but you have to tower early to protect yourself, and against anyone decent you'll be on the defensive the entire game. I don't think I saw any top ranked player who played UK much, if at all. Just a bear. Of course, in newbie games, UK is the best civ. Just chop wood and build econ buildings (Food Warehouse, Mining Camps) and watch the cash roll in. I can't tell you how many times I've completely trashed newbies trying this because they've never played competitive games before - they think an early attack (rush) is a dirty tactic... And of course in larger MP games, UK is a potentially great ally in the pocket... they can boom and then you're doomed. Adder has made a living doing this, even recently in a friendly FFA game No one listens to me, though.