Tynne has been bugging me about this, so here we go. These are the ports that I have opened. With them closed, the NAT relays kick in and I lag to everyone. With them open, I only lag when my internet craps out. If you're lagging to about half the people in this game, it's probably this more than anything else.
7103
7102
7101
5063
5406
All both TCP and UDP.
I don't know if you actually need ALL of these, but I have no reliable way to run tests to see if fewer are needed.
HOW TO MAKE THIS WORK
Step 1:
Set yourself up for a static IP address. Ask if you don't know how. You can kinda get by without this.
Step 2:
Go to your router and forward the ports to your computer's IP. It may be under "Virtual Server", or "Services on the Network", or something similar.
If you have no idea, just keep asking questions until you get good information.