I´d say UK, too.
We usually start in '38 when playing in LANs. UK starts with about 14 Infs, 2 LightArmour(1) with hardly any strenght and about 25 garrisons it´s not allowed to move until an event triggers. Until late '39 you´ll usually face 3 enemies: Germany, Italy, Japan (+puppet NatChi). Combined, they got mightier fleets of different kinds (so you got to research ASW, battleships and carriers) and will enourmously outnumber your ground forces (in the last game they had something like 350 divisions combined until then). Your airforce usually is older than the germans but if used right, you can do great damage on Japan and Italy.
And your manpower is not great, either. Killing manpower bonus ministers has my top secret service priority.
IC-wise, it´s great. You don´t have as many as Germany. But with full hawk and fully market-oriented you´re the most efficient economy in the world.
My conclusion: The longer you can stand the ground, the better your chances to hold on will be. But in my opinion it´s impossible to begin an offensive without american support. This doesn´t mean you should just stay in you provinces and wait for attacks. You´ll have to plan counterattacks, look for small opportunities to bother your enemies....But you should not have the illusion of breaking the axis on your own.
In my opinion UK is the most fun to play, because
1. I love the navy game,
2. You´re really into trouble,
3. You got the moral bonus of defending democracy,
4. Your in the war from the very beginning