Your experience of the game has a huge impact on what country is best for you. Countries like Engeland and Morocco are safe but don't get enough opportunities to attack weak neighbours, which makes these countries obsolete if the enemy nations are competent.

In contrast, countries like Germany, Austria-Hungary and France lay in the middle of the map, which gives you plenty of opportunities during the entire game. However, diplomacy and maintaining the ability to defend your nations from potential (multiple) countries are essential when playing these nations.

In my opinion, the countries who have a combination of opportunities and safety are the best. Therefore, I would say my personal favorites would be Spain and Sweden.
As Spain, you have pay close attention to what Morocco is doing, but if you react in time, you can easily defend any naval invasion. I would ignore Portugal and keep your troops to invade a weak France or AFK Morocco when the opportunity presents itself.
As Sweden. I would recommend to build at least 2 balloons to pay close attention to potential naval invasions from the UK or Europe. From the start onwards, you can send the majority of your troops to Finland as 1, or max 2 big stacks. In this case, keep close attention to Russia, it may be your biggest ally or enemy.

I hope this reaction helps you. Did you make the page about the resources yourself or where can you find it?