So far the Samsung has proven itself to be a very stable product. Although the firmware cannot be updated but that might change in the future. Instead, having to constantly update the FW only proves that the company did not come up with a rock solid product in the first place. Those comments I have read about the Samsung having errors, the drives were from a pre release batch,pulled from other Dell computers and not retail versions.
According to official specs, it loses to intel in terms of random speeds and to the OCZ for the sequential read. Still it has one of the largest size and the faster sequential write. That aside, it is a reputable drive known for stability and solid performance. So with the rising cost for Vertex, I would recommend it over the Vertex.
You're basing it on official specs instead of reviews and user experiences? Vertex has 250GB , so that's not a valid reason to get Samsung over Vertex (fact they both have same storage, 256GB/256GB, its just that Vertex marketing decided to show the usable size instead of all size, a few GB are reserved in case some of the NAND fails and some are used for wear leaving data). Faster Seq write isn't anything to write home about, it is almost the same. The random performance according to some users benches and reviews is lower than both Vertex and Intel together. It may get better over time with firmware updates, Summit and other SSDs based on Samsung's controller WILL have the ability to update firmware, just not Samsung OEM SSDs.
The only thing Samsung has going is what you said in the end, solid stable performance over all and reliability, Samsung makes good SSDs. It is in top three, I would place it at #3 next to #2 Vertex and #1 Intel. (all of them are excellent) but those "preproduction" SSDs are still everywhere. Remember you can't actually buy retail Samsung drives directly, they only source it to OEM which is why you can get it from Dell, Corsair instead.
Also, Samsung errors are possible results of pre-production firmware are my guesses as well but so far there are still people getting issues with both Samsung and Corsair. https://forums.macrumors.com/threads/658571/
Once those "preproduction" ssds are out of the inventory and all freshly new stable SSDs are in stock, that's when people should buy them.
As for rising cost, that's the result of NAND prices going up, not OCZ's fault. It is still under 400$ everywhere in US for 120GB, which is what I bought it at. So nothing surprising here. Samsung P256 is however cheaper here. I would get it for 669$ over Vertex's 250GB for 950$. But I don't often need more than 60GB for system drive, thus for 120GB vertex is very nice.
I do want to mention even Vertex and Intels have their own problems. Right now Intels are the most stable with the latest firmware. Vertex still not the most stable for Macs but seem to be less problematic then the preproduction Samsungs.