The samsung has been cheap for like, 4-5 months now probably, so its hardly cheap because of that also, the 840 is faster in benchmarks... barely, real world performance you won't even slightly notice it. Sure the price will come down eventually but anyone that spends 50% more on the same capacity on the new version is mental.
Outside of async memory versions of drives which do seem to suffer from much more severe slowdown as they fill up, you can barely tell the difference between any of the drives available in the past 2 years. Cheapest 256gb should get your money.