So I was reading the tech article on this site about gear ratios, but I still don't truly understand.
I know that a 3.73 is better then a 2.7(fill in the blank) but why.

At redline, which gear is faster, better, and why?

I have 3.23 gears.

 

The higher the ratio is numerically(3.73 vs 2.7x), the more engine torque is multiplied at the rear axle. The result is faster acceleration, but the engine will run at higher RPM's on the highway and use more fuel overall. The lower the ratio is numerically, the slower it will accelerate. But your engine will run at lower RPM's on the highway, and use less fuel. All of this is somewhat defendant on your engine and transmission however. If you have a weaker engine(like a 4 cylinder for example) it won't have the power to take advantage of the higher gear ratio's ability to accelerate faster. The transmission also changes gear ratios to shift gears, so you can end up having to shift sooner or hold a gear longer depending on its ratios.