I like the spectacle and excitement of a rocket launch, so I picked FX. I like to see the rocket in flight, so I don't really need or want it to go too fast. I enjoy watching the deployment, so I do not need or want it to be too high at apogee. A good smoke trail makes the rocket easier to see and track, so I like that. Colored flame and other effects are cool to watch. I'd rather launch a large rocket to 1,000 feet on a pillar of smoke and fire than teleport a small rocket out of site.
I think if I were more into the engineering and performance side of rocketry, working with electronics, dual deployment, trackers, etc. then ISP would mean more to me, but I'm not into that yet. Probably my first foray into electronics will be with air-starts --- again, for spectacle and excitement, not performance.