For Recipe testing, i think the Hadaly is really good. It gives a very good impression about how a mix turns out right after mixing. I also prefer the old Petri V2, because i used it so much and it's simple and easy to rewick.
For me i also use a Taifun GT4 and a Kayfun V5 and a Squape X, because besides RDAs, that's what i use most, and these 3 RTAs are the best flavor machines on the market right now.
MTL recipes i do test in the Berserker MTL RDA and an old Squape Rs.