I am not quite sure what the best booming civ is, I would say German, or maybe British I guess (since with a higher cap rate, they can go a bit longer before they start looking for com cap increases). You'll have to experiment a bit, or listen to what the other fine folks are saying here.
As for defending the rush, if you can, research MIL1, build a tower, research attrition, and stock the tower with a couple of archers. Build more towers if you've the time/resources. But, it's a double-edged sword. Sure, the one rushing you is taking the risk at being behind in economy, but if you go all out defending, you'll be in the same boat basically. And... if there isn't a rush, they'll be booming ahead of you.
Do the MIL1, build a tower, research attrition (if you can), and when the attack comes plunk a few citizens in the tower, and more in your city(ies). If you properly place your tower, then you can protect the citizens that are still working, and the city will also open up on the attackers. I tend to leave my citizens out working, unless they are directly in danger. Too many times I've seen people rush all their citizens into their cities and towers, which accomplishes almost exactly what the attacker wants. If your economy grinds to a halt, then you won't be building the troops to attack with.