I normally recommend Samsung. Intel, Crucial, and Plextor are also worth considering.
Samsung did something different this time. This is the first time Samsung released two different models - the 840 and the 840 Pro. The 840 was designed as a value or mainstream model suitable for ordinary everyday use. The 840 Pro is Samsung's flagship model. Both models use the same controller but the memory is different. Samsung decided to use triple level cell (TLC) memory in the 840. This is the first time web sites that publish technical reviews have seen an ssd equipped with TLC memory. A concern has been expressed that the memory will not last as long as other types of memory. So far all we have are estimates about how long the memory will last. It appears the memory should be okay for ordinary everyday use.
I maintain the ssd database listed in the sticky at the very top of this forum section. Here is the link:
You're not going to see much, if any, performance diff, so it boils down to reliability and least user problems.
I have the 256 gig Samsung pro, and a 256 gig M4 and Samsung 830.
AS SSD shows my M4 with an overall score of 700+ and for the 256 gig 840 Pro it is 1100. Big diff between benchmarks results - but I'll bet you could not tell me which is in use in my laptop.
ONLY reason for replacing the M4 in laptop was A) reduced power consumpton and B) had to verify - had too spend the cash, or let it burn a hole in wallet and to keep the moths from eating my hidden stash - LOL
Concur with recommendations of Samsung 830/840 pro, Crucial M4 (DO NOT buy crucial m5 or V4), and Plextor. Normally no longer recommend the Intel 500 series - great reliability, but my personal preference is to avoid Sandforce based controller SSDs (NOTE Intel's 510 was based on a Crucial controller, but switched to SF with the 520). I have both Intel G1 and G2 and both are still going strong (Both based on a Intel controller)!
Dont get the 120gb 840. the write speeds are down into hdd territory, about 120mb/s iirc. the 250gb does double and the 500 does about 330mb/s.
Yes, the write speeds are low. No doubt about that. Hard OCP published two 840 reviews. In the second review while addressing memory longevity the author suggested that using the Samsung SSD Magician utility to increase overprovisioning would increase memory longevity and improve the write speed. Unfortunately there was no additional information about improving write speeds. I have not run across any other reviews or articles which confirmed the information about improving write speeds. Perhaps one of the forum readers with an 840 could do a before and after experiment.