I guess there are multiple ways to deal with this.
You could go along with the balance of writing all three stories at once and get the best of both worlds with writing your favourite stuff while also pleasing your entire readership. Cons being, as you've stated, it's difficult to write three books at once and still go full throttle.
Or, you could write what you enjoy most, it being a hobby and all (probably Black Tarantula lol) and thus your work would be better since you care more about what you're putting out and so the complete story would be something that side of your fanbase appreciated a whole lot more, as do you. Cons being, you may lose some readers who only care about a particular story and whatnot.
And the other option is to write your most popular work first, which would please the most people in your readership. In this case that would likely be Fundamental Forces, and as you've stated, it would take the least time to finish too so there's that. Cons being, you may want to work on other stories still and such you might get burned out.
Or maybe you could lessen your workload and write two stories instead of three? I don't really know, just tossing here. It's all up to you lol
Either way, I enjoy literally all of your stories so whatever you do I'm here for it. Try not to let this all bog you down :)