Would like it to be left/right foot universal and adjustable.
Most all are left or right, but do come in general sizes (S/M/L)
There really is no “best” since design components of one (no posterior part for ex) is helpful for some, but not for others. Some (like the Strassberg sock) dorsiflex the toes as well (good for plantar fasciitis) causing more numbness and not helpful for other issues like achilles or soleus pathologies.
In general, my favorite is the DonJoy Procare Dorsiwedge (you can find online from $80-100 or so). Comfy and can treat a variety of condition that typically affects triathletes and other crazy type-A individuals … 
Thought you might find this interesting - Ethan Brown’s blog talking about PF - http://emantri.blogspot.com/
Hope this helps.