Thorichthys socolofi are the smallest, probably one of the most peaceful of the genus as well.
I have kept all Thorichthys I think, bred aureus, macculipinnis, meeki, pasionis, socolofi, sp.mixteco blue, sp.mixteco gold & callolepis.
To answer your question on best Thorichthys, it is all of them, each and every last one is worth keeping, for me I have always had a soft spot for T.mixteco blue:

Or helleri:

But I have kept some stunning other Thorichthys like these aureus for example, get good stock from a trusted breeder (so no hybrids) and you cant go wrong.

On my most wanted list is actually affinis, dubbed a drab meeki, but to me they look great!
I can post more pictures if you would like.....
Dave

