The Samsung 840 Pro is preferred over the Corsair Force GS. The Force GS is equipped with an older SandForce controller. SandForce has not introduced a new controller in over 2 years.
The OCZ Vector rather than the Vertex 4 is the direct competitor to the Samsung 840 Pro. Samsung has a stellar track record in terms of quality, reliability, and performance. Part of that is due to the fact that Samsung does its own reseach and development and manufactures all of the ssd components and firmware used in their ssd's. OCZ have had more than their fair share of problems and issues.
Modern 3rd generation SATA 3 6Gb/s solid state drives form a fairly tight performance cluster. A user would not normally notice any difference during typical everyday use. A user would have to run synthetic benchmarks in order to measure those small differences. The synthetic benchmarks were designed to grossly exaggerate those minor differences. In addition they do not always accurately represent real world use.
I maintain the ssd database listed in the sticky at the very top of this forum section. Here is the link:http://www.johnnylucky.org/data-storage/ssd-database.html
Scroll down to the brands and models you are interested in and follow the links to the technical reviews.