You can put me in the four parent cross camp. I can't say what four parents because I already have a bias, working with at least one of those, and very happy with the variety produced.
Aside from the genetic diversity level, as I understand it you have a better chance of breaking linkages and producing something unusual in a cross between two F1's or unstable generations.
For maximum diversity, you could say, lets have a beef, a heart, and parents with other exemplary traits that are important to your situation (cold tolerance, heat setting, disease resistance, or other survival trait). At least one cherry or small fruit in the mix because we all know they endure extremes and produce when others don't.
Gotta have sweet, gotta have umami, gotta have tang if you're going to have all tomato tastes in the bag. Gotta have yellow, black, and pink (or purple) to get all the colors. OMG I forgot orange. You may need more than four to capture all the orange genetics! No joke.
CRISPR is cool but nature is cooler. The ability to adapt, is the opposite of CRISPR.
Besides the 4 parent crosses, I would recommend stressed fruit crosses, for maximum chance of a genetic leap. Late crosses when it's too cold. Midseason crosses when it's too hot. Nature provides the motivation for spontaneous change. Tomatoes are a goldilocks fruit, motivational exercises are a good thing.
