I haven't tried either, but doing some research into which SSD to put in my i7 iMac I came across the following very interesting set of tests on the Crucial M225 vs a cheaper Crucial and the OWC Mercury Extreme:
http://macperformanceguide.com/SSD-RealWorld.html
The OWC SSD uses the relatively new SandForce SF-1200 chipset, and as such has a LOT of "overprovisioned" space--meaning flash storage that exists, but isn't user accessible, instead reserved for in-the-background replacement of the user-visible storage space when chips flake out. The upshot is that, in theory, they're much faster and longer-lived than other drives (10M rated MTBF for the OWC instead of 1.5M for most others), but also much more expensive in terms of $/GB, since you're literally paying for an extra 20% storage space you never get to access directly.
If you look at the graphs in the article above, you'll note that the OWC (and presumably any other SandForce-based drive, such as those from OCZ) remains at full speed even after having a lot done on it, while the M225 starts having performance "hiccups" and dropoff. Some of that may be due to the lack of TRIM support in the MacOS, meaning it might not be so stark a difference at some future date when the MacOS is updated to take better advantage of a SSD. On the other hand, right now, there's a clear advantage, at least if you're going to be pushing the drive and/or adding and deleting a lot of files.
To a lot of people, it probably isn't worth the extra expense. To me, the 5-year warranty and added reliability, coupled with the VERY flat performance curve, is worth the added expense (it's not wildly more than the M225), and I also like OWC as a company.
Here's an Anandtech article about an OCZ drive that also uses the SandForce chipset:
http://www.anandtech.com/show/2899/1
Edit: And here's a Mac-specific BareFeats article comparing the OWC drive to the M225 and a few other high-end ones:
http://www.barefeats.com/hard130.html
...in which they're all fast, but the OWC has a significant margin over anything else.