I just played for a half hour and paid attention to what I was using, if anything. The vast majority of shots either used the basic diamond system, or the side rail numbers system like I pasted in above, or using the 2nd short rail contact point to figure out how to get on the right track. A ticky came up, that's using the exact same side rail numbers system, you just have to add an adjustment depending on the angle you're coming in on. and of course knowing running lines/tracks. Plus system came up twice. I use these all the time so I barely even think about them. They're barely even 'systems' to me anymore at this point. With the side rail number system, I barely have to wait for the first object ball to stop rolling. I see it's coming in at 2 (or 20) so I just know where the cue ball is going to go if I hit it with 1/4 or 1/2 hit. Don't even have to think about it, just focus on hitting the cue ball right.
I know a bunch of systems because I just think they're cool. But most of them you don't use that often. When some odd shot where the two object balls are together and there's no easy natural shot comes up, it's always a good feeling to whip out some system and make it.
But I think you're best off having a small handful of the most useful systems, like the diamond and plus and running tracks, and just really working through them and the adjustments to them. Like I said, eventually they stop being systems and just become part of your game. You don't even have to think about the shot much anymore, you just know where the cue ball is going if you hit it right. It frees you up to worry about kisses and speed and all the other stuff.
Of course, you can always pick up super easy to remember systems like this one. Count the distance between the two object balls 20 to 60 = 40. Divide by 2 = 20. That's where you need to hit 'through' the diamond on the short rail, with running English, to make the shot. If the second object ball was at 40, the distance is 20/2 = 10, you have to hit 10 on the short rail. The rail numbers are the easiest thing to remember, each diamond is 10. That's it, take one minute to memorize that and you'll never forget it.