In my experience,Southern USA is one of the best nations for me. I only need to worry about one border; The one with Central USA. And although Southern USA has a lumber shortage,then can just invade Newfoundland's double lumber province,right next to Southern USA. Also,if Morocco and West Algeria go inactive/become your allies/are simply not just interested in French West Africa,you can go ahead and seize French West Africa for the oil and additional resources.
Romania is also working out pretty well for me. I have joined a Tutorial game about 4 days ago (Now its Day 18) and Im in the 5th place,with my coalition members in the 1st and 2nd places. Romania simply has balanced resources,and although you have a shortage of coal to build railways with,you can always find a lot of coal in the Stock Market for cheap prices. There is also Bulgaria to the south,which can be invaded for resources (If you wish,you can wait until Greece dishes it out with Bulgaria and conquers Bulgaria,losing troops along the way,and then you can swoop in and take Bulgaria from Greece easily,and Greece itself too. This is assuming Greece is not your ally,or is not interested in Bulgaria,of course).