As long as I can be certain that I will be getting SATA III read/write speeds then I will get the Samsung, otherwise I may as well just go for a SATA II SSD.
While you should get the speeds, you probably would not notice any difference; unless you have very very large files. Think of it this way:
Your on a motor way with a 100km/hr speed limit (you SATA Interface)
You have the choice of two cars - one tops out at 50km/hr, the other at 100km/hr. (The drive).
You, however, only go 100 meters before you stop (loading a normal file). While the second car will get there first, the difference will not be noticeable.
No, if you are going a 100km, then there is a difference. (Loading large files.)
Not trying to sway you one way or the other, just providing a real world perspective.
As for the Crucial, their forum has some discussions on that drive:
http://forums.crucial.com/t5/Solid-State-Drives-SSD/What-a-nightmare-Crucial-M4-512GB-DOA/td-p/61027
It looks like it is fixed, based on the last post. I can't verify that since I have a Patriot SSD.
Whatever SSD you get you will be happy. Enjoy.