Ok, serious now, here's my advice.
Avoid the Spitfire IX if you've been online for a month or more. Its a crutch. Same with the LA-7. Yes, you'll learn things like views and basic game commands and how things work and that's great if you're brand spanking new, but for learning to fly combat, it becomes a crutch. The Spit IX is a very forgiving aircraft and if you don't pay for your mistakes you'll never know that you're making them.
If you want to learn air combat through the school of hard knocks, fly the 109s or the Yak. You'll learn how to manage your speed, manage your ammo, and gunnery (because convergence won't matter and you have a small ammo load). The 109 will teach you how to manage your energy and the Yak will teach you how to maneuver in close to your target. If you can kill with either of those planes, you can kill with just about any plane. Except the P-38.
The P-38 requires a bit more thought. It takes some skill in working trim tabs to break out of compression, flaps to help with lift in a turnfight, and WEP to manage airspeed. The 109 will help you recognize the signs of compression, and the skills you learn with the 109 will be applicable with the P-38 as well.
Ok, that's all I have for now. Its a start.