@scottalanmiller said:
So many vendors, products, techniques and approaches exist because most are the "best" in different combinations, at different times for different scenarios.
Exactly. The best solution is the one that's most suited to a particular application/environment/budget. There never is a universal best - which, of course, is exactly why that perennial favourite of the interwebs - the "Top X Best" list - is pretty pointless.

What capacity to do you need? The 216 provides up to 16TB of raw capacity while the 1515+ provides up to 120TB (when used in conjunction with expansion chassis)..