I used to use M4s, and have had no trouble with them.
I switched to Samsung because of price and good performance (no real difference in performance, but the spec for the Samsungs were good). I also had a feeling that Samsung woul design a manufacture a good quality product.
I`ve now fitted way more Samsung SSDs than Crucial, and like the Crucials, they have been very reliable.
Having said that, reading this forum does seem to suggest that failure of Crucial SSDs is more common than Samsung failures. I know that's only anecdotal evidence, but it leads me to believe that choosing a Samsung SSD is a good choice. Only time will tell for sure, but so far, so good.