I generally teeter around 0.18-0.3 ohms on a mech. I like to stay between 60 and 100 watts. The SMPL v1 is my workhorse mod. My favorite atty in terms of airflow, deck depth, and chamber size would have to be the Mutation X v3.
Lower resistance for thicker wire, higher for thinner. It also depends on the atty. For instance, in my Mutation X v3, I would never run anything below .22, while on the v4 or the Troll, I can go as low a .16 because they have airflow and chamber space for days, though I tend to build a little higher than that in those. I like 22g at 0.16-0.18, 24g or dual parallel 26g at 0.2-0.24, and dual parallel 28g at 0.26-0.3. None of those builds ever do me wrong on any RDA I own.
My go-to build is a dual 24g @ 0.24 ohms; 7 wraps, 2mm id, preferably in the Mutation X v3. I do a wide variety of builds in a handful of different RDA's, but I inevitably come back to that when I want an all-month-vape. Generally speaking, I seem to get the best performance out of simple, round wire builds.