Personally on my own system I have 2tb of internal storage (2 - 750gb and a 500gb HDD) and another 2tb of external storage (2tb via eSATA)
My system drive is a 120gb Kingston that I paid $59(shipped) for.
The day that I bought it was actually cheaper than a hard drive
the same size and in point of fact than any HDD sold on Newegg
IF I get as long as two years out of it I'll be happy with it, but I fully intend to replace it with a 256gb as soon as I can get one for what I am willing to pay for it.
In short that equals a 256gb Vertex4 or similar for <$120, I figuire that'll
happen in 2-3 months.
Longevity and performance of an SSD is pretty much related to the USED space relative to the TOTAL space.
if you are running an older Motherboard that only supports SATA-3.0 you should still buy a SATA-6.0 drive, even though you will not get full performance out of it you might when you upgrade to a newer computer that does support SATA-6.0
On a SATA-3.0 controller the additional performance offered by a larger
SSD likely isn't noticeable.
Plus there is always the temptation with a larger SSD (a 512gb)
to use it for storage, which IMO is a mistake.
a 240gb or 256gb is what I currently consider "ideal" for a windows7 operating system running on a SATA 3.0 controller.
NOTE: I bought a 120gb because it was CHEAP and I considered any SSD smaller
than 120gb to be not worth owning let alone buying.
In my case it cut my boot time by 75% (I recently discovered an intermittent SATA cable to one of my HDD's that was slowing drive recognition time) and cut the time for my older stand alone e-mail program to load (it is installed on a 2gb partition on the SSD) by 90%
I'm sure if anyone disagrees with what I've just said here they will
say so, and I'd like to see if there are any flaws in my logic and
understanding of the various factors for choosing the "right"
SSD for "the average user".