CV, welcome.
I've had four or five RMK 'Fireman's Special' models knives to date, all in either four finger or 'Border Patrol' (BP) handle configuration; for me, the BP's have far and away been the best ergonomic choice - haven't had a single finger groove (SFG) handle version to compare with though, so there's another option too...
Here's the thing; with most of the full-tang models (specifically the #14, #15, #16, & #16-17) the handle style on any given, individual knife may 'fit' you, while others don't. Same handle shape mind you, just something slightly different that fits your hand better'n others...
Point being, it may not be the handle style that works for ya - rather, the dimensions of said handle. I buy a whole lot of RMK's just to find the few that fit me...and when I find those knives, I don't sell 'em.
As far as your question goes tho'...I've found the BP handle shape to be the most flexible. Hope that helps.
-S