Of these 3 stats; which is the best indicator???? Thanx.

Best indicator for what?

I still don't understand what is being asked, and maybe that's just me, but smart-*** comments don't help.

IF the OP is asking about the best stats to use when comparing one player versus another in SLB, then I would say:
-- None of those stats directly factor into the algorithm
-- I never even look at RC or SecA
-- I sometimes use RC27 as a starting point, but definitely not as the be all and end all

RC is a function of OBP and SLG in its most basic form, so depending on how I’m trying to create a team I’ll sort by OPS# or RC27 and control for $/PA or total PAs in a band. Personally I don’t love paying for high bb hitters in the sim so I’ll then look to avg and slg as the components of that top level search and build accordingly. At the end of the day you want as many RC as possible, but the way to get there is by maximizing your RC27 for your $ and usable PAs (for this reason I basically don’t count RC over 650 PAs because you’ll never use them).

In my entire existence of WIS, I’ve never looked at real life RC or RC/27 (I often look at the PH RC to get an idea of what to expect in the sim) and I’ve never looked at SecA as a stat period.

I'm routinely average, so take my opinions with a grain of salt lol