I don't know the answer to which TB-2 dock is "best," but it may be useful to know that you
can use a Thunderbolt 3 dock. It will work only if:
- You use an authentic Apple Thunderbolt 3 to Thunderbolt 2 adapter, AND
- The Thunderbolt 3 dock has its own power supply (the adapter does not pass power over the Thunderbolt cable).
Don't buy another brand adapter; from what I've read they only work one way (from a TB-3 computer to a TB-2 device). In contrast, the Apple device page say