I would've suggested ANY 250/256GB over a 120-level drive just because of the added controllers. In many cases it's the sweet spot for performance (relatively), and often doesn't add even close proportionally to the price where-as 512GB may (sometimes) saturate sata leading to a diminished return, and the total price (considering many probably just want one 'big-enough' to run the o/s and some apps quickly) at 512GB certainly is a factor for many. It's a no-brainer imho, for absolute value grab a ~$100 250GB-level drive.
The same mindset could be used for either buying multiple drives outright or upgrading in time to a RAID: 3x250GB drives may cost less and saturate the interface for speed; 2x500GB will often do the same (as one 512GB drive is often almost there by itself) while getting slightly more space through less drives and similar to slightly lower cost per GB.
A couple good/cheap options are always the reputable Crucial mx and now bx100. MX has gone on sale often, BX replaces it and starts at around the sale prices of the MX. It is currently $100 in the US, but will probably become even cheaper quickly. I think Crucial/Micron will consistently try to keep the prices low-enough that they are often not in direct contention with the 850 evo (which itself has dropped in price recently to around $120 and has gone on sale for around $100). Wait on a sale for a crucial/samsung drive so that the value/speed proposition is tilted in the favor with accordance to the performance difference and/or your budget.
