Thanks for the comments.
The 240GB Vertex 3 is the fastest, as it has the max parallelism from the NAND to the SSD controller, so the 120GB version isn't quite so fast.
The Agility 3 uses the same SF-2281 controller found in the Vertex 3, but uses synchronous NAND, while the Vertex 3 uses the faster ONFI 2 NAND.
There is now a 60GB version of Vertex 3 as well.
All OCZ SSDs using the SF-2281 are lightning fast in any case.