Generally a OS + Program SSD is preferable to a Caching SSD.
Advantage of OS + program SSD is everything on it is speeded up, and YOU get to choose. Only requires ONE drive bay (laptops). Disadvastage is size, ie a 500 gig SSD is expensive.
Advantage to a caching SSD, Retain Large storage space, But what is NOT in cache is NOT speeded up - It's biggest disadvantage and you are at the mercy of the algorthum that chooses. And for Laptops requires TWO drive bays!!
Bottom line - If Have two drive bays the go SSD for OS + Programs and use your HDD for storage. IF single Bay, SSD (=> 128 gig) for OS + programs then get a USB3 2 1/2 enclouser and put HDD in that.
Myself, I have a 2 bay laptop (Samsung 17" i5-2410m) and first swapped the HDD for a SSD (used the HDD for storage). later stuck a 2nd one in the 2nd bay for "fast" storage.
Which One. Samsung 830 -> Curcial M4/Plextor M3/M4 -> samsung 840.
The performance of all are very close, along with Low User complaints ratings. So Choice is Tied to Lowest power consumption (barring price differences).
The new Samsung 840 has improved performane (at least in benchmarks), while cutting the Power consumtion from the 830. NOTE: power consumtion only a factor when used on battery. The 840 is going to be the Higher priced one, so if cost a factor between the Samsung 830 and the Curcial M4, excluding power consumption, which ever is cheapest.
Have 3 Curcial M4's, 3 Samsung 830's and 2 Agility III's
Only recommend drives that use the SF22xx controller if at a bargain Price.
PS newer intel SSDs use the SF22xx controller, but does have a rep for a very reliable drive - still I normaly perfer the drives I quoted over the Intel drives.