Best way of attack?

I find a good combined arms attack force works the best. But you need to account for the type of attacks you are doing. For example if you know your going to encounter heavy resistance, and speed is not important use a nice mix of artillery, heavy tanks and medium tanks with a few infantry for cities. If speed is of the utmost importance I like to use tracked artillery, light and medium tanks, tacked AA and jeep infantry. This allows you to move quickly through enemy provinces and cap. But there is many different ways to accomplish the same goal, just always check out your opponenet, and get a good idea if they are a well experienced player or new.