United States hands down in my opinion, for a few reasons.

1. Insane economic potential - (~200K tons first day with much room to grow)
   
2. Fear factor - most people will want to befriend you and that allows you to develop in peace
   
3. Homeland defense - lots of time to see a invasion fleet coming
   
4. Pretty weak neighbors - nobody around you can hold a candle to you except maybe Brazil, and even that nation is fair way off and will likely be distracted by his own matters.
   

You are a good player. Japan is a great nation to win solo if you know how to use it. Asia is in the palm of your hand, and the US will lose with the economic might of Asia on your side.

It depends if you want a SURE victory (pick USA) or a QUICK victory (pick Germany). The latter is more of a challenge, but if France, UK, USSR and one or two smaller powers go inactive soon (and they often do), you can control the economic might of Europe soon and no one can stop you.

I played that map three times so far and I've always won, one time being part of a coaliton containing the UK, Spain and Germany (me). The other two times I got a solo victory playing the UK. My ally, USA, went inactive and left me hanging, collecting almost the entire map.. I beat Central Europe twice by spamming rockets, marine and aircraft. Pretty much grinded their infrastructure and focused on a prolonged war. In one of the games I steamrolled France at the very beginning and Germany was no real issue because these guys always invest into tanks and attack countries like Poland and Ai first.

The only real Issue I had was facing the Soviet Union as Germany 1v1 - that war took like two weeks and I beat him at the end cause he tried too hard, being overly aggressive and insulting me via PM for such "scummy tactics" of not allying with him. Granted, the players I had to face on my three playthroughs were clearly not the best. I'd say UK is pretty great cause you have time to build up.

In my experience of Historicals, you can pick a major, then wait a couple of days, then 'Retire' in the newspaper for victory.

Poland is the best. If you can crush Germany when he tries to invade you.

Ono the weakest armies in the game? You should see the starting army of Persia or manchukuo.
Venezuela is the worst most prolly.

weakest land strikeforces of top 5 countries in HWW map. If Canada and Mexico team up and attack USA in first 10 hours after game start, USA can not win. By same skills and online time of players.
But yeah. USA is one of easieast country in HWW. There are few players who know how to kill USA at start of game. Every other have fear of overweight enemy.

USSR is even more easier.

i won HWW map many times, solo and with coalition win. I always use a country in middle east like iraq, persia, turkey, or saudi arabia. From that position you can choose to focused in many front like balkan, central asia, northern africa, or sovyet (they almost goes offline in every game, and easy to take). Suriah also a free land because england and france can't stand to defend it

Once you get some experience in HWW, try Spain. It's prolly one of my favorites, but requires patience and a good team. Strat is to rush Portugal (don't bother getting the colonies, most often South Africa takes them), build up your industry, and attack France in conjunction with allies (it's harder alone, but possible if France is a newbie), take all French African colonies and Europe is your own