What do you mean by fastest? Do you mean synthetic benchmarks or real world performance? What exactly do you do with your computer? The answer to your question will depend on your answers to my questions.
It sounds like you will be doing professional work involving incompressable data. If that is so, then you'll want to consider an ssd with a Marvell Controller rather than an ssd with a SandForce Controller. The SandForce Controllers were designed to be fast with compressable data while the Marvell Controllers are fast with incompressable data.
Real world performance. I do software development, video conversions and photo editing. I want my computer to be very zippy. It doesn't harm to get a faster SSD than my needs. I have the money for it.
While my OS drive is a Vertex 3 240, I use a 256Gb Crucial M4 as a video encoding scratch drive and it does a great job. Cost may not be a key factor, but I got the M4 256 for only $170 -- so check the price site that JohnnyLucky linked for the best deal. They seem to go on sale weekly.