Re: Rogue/Fighter AC
I'm not sure why people think the Rogue/Fighter won't have good AC. Dexterity should be your primary ability, as it gives you +1 AC and +1 BAB with Weapon Finesse.
Comparing armor only, your AC is only one worse than a fighter in Full Plate, given both of you have sufficient Dexterity to max out AC (8 armor +3 from Dexterity - Mithril Full Plate; 4 armor +6 from Dexterity - Mithril Shirt).
Where does the Fighter/Rogue lose AC? By using two weapons. I think this is a poor choice, even if you have high Sneak Attack. You're better off using a magic shield (+2 AC for a Heavy Shield, and more magical bonus), your attack is not reduced by -2, you have spare feats to put into other things (Weapon Focus, Weapon Specialization, etc.), and more money to spend on other equipment.
My Rogue/Fighter of 17th level has
Ring of Protection +2, +2 AC
Heavy Shield +2, +4 AC
Mithril Shirt +2, +6 AC
Dexterity 22, +6 AC
For a total of AC 28. (Relatively low magic campaign, otherwise those magical bonuses would be higher.)
Throw in the Dodge feat (+1 AC vs. one opponent), and Expertise (for when you need to defend vs. high BAB opponents), and your AC is as good or better than your fellow tank.
But my Rogue/Fighter doesn't have the HP ... mostly d6 HD and Constitution of 12 ... No way that my Rogue/Fighter can stand up to a high BAB/high damage opponent, but that's what running away if for.
