For years I too lived by the "southern storm" rule, but after a while it proved itself to be a crapshoot at best on any given day. Jim Leonard once told me "stay with the storm you're on," and I think that's pretty wise. For me, the wisdom in this approach is that you really don't know what will happen, and going out of your way to miss something good makes a lot less sense than missing something good because you stuck to your guns.
Of course sometimes there are situations where you just "know" what to do. You might not get a tornado, but the decision ends up bagging you the better storm. Certain situations will deictate my decisions, based on storm behavior "rules" or "for sures" such as a splitting cell.....I'll take the right mover (southern storm) every time. Other situations where there are two discrete cells, that's always a gut call for me. If I think one storm is better than the other, I'll go for it regardless of roads or distance. The only factor that will make me choose the "other storm" (the one I don't want) is darkness.
May 31, 1999 we had targeted Shattuck, OK and had been there all afternoon. We saw what was the beginnings of the Meade/Sitka cell and headed north for it. A glance over my shoulder showed a fully-developed supercell, much further away to the distant southwest. I didn't even think about it, that was our storm. Later that evening we intercepted three tornadoes in SW OK, while the circus was raging in SW KS. I think I can count the other chasers who saw those SW OK tornadoes with us on one hand.
May 3, 2003 we came into Paducah, TX with a storm bearing down on us from the south. I called Dwain and he told me the storm near us was a left split, and that the right split was about 50 miles south of us, and the only thing on radar that looked worth going after. Without even considering it, we blasted south for a storm we couldn't even see yet. As several other chasers were parked south of Paducah with vidcams mounted, pointed at the storm, we blasted right into the core and out of town. Some of the looks on their faces have made me wonder to this day if they knew about the southern split. Eventually we came into visual range of the southern storm, and before the day was over we'd seen five tornadoes, along with one of the top-three storms I've ever witnessed.
May 5, 2001 we had been on the north storm since the first cumulus, and had tracked it for well over an hour as it moved towards Rocky and Cordell. A new storm blew up to the south, and we pulled over to analyze. The northern storm was due north od us, the southern storm SW of us. We had cool inflow feeding the north storm, while chunks of cloud were being ripped away from it's southern flank and pulled into the southern storm. Looking due south, we could see rainbands bowed nearly 90 degrees, riding inflow into the southern storm. We sat and debated all this and the decision was made to go for the southern storm. later that evening the north storm produced a pair of beautiful purple tornadoes while all we got was a linear mess. The northern storm had encountered a boundary shortly after we'd abandoned it, something we hadn't been aware of prior.
It goes both ways, and no one can predict which storm will tornado from one moment to the next with exact certainty. This is just one of the things that makes chasing so much fun, the little challenges we're faced with every step of the way.
