I like both, although sometimes the plasticine smells.
Clay feels more artsy.
Plasticine more childhood fun.
Clay…the pressure not to mess up.
Plasticine…goof, smash, restart.
The thing is they can be used together. The plasticine as a rough draft. Something to practice and experiment. Move to the clay when you’ve found the path you want. Sure, some may call this overkill, waste of time, but for some of us – me – it frees us to make mistakes. Frees the critical brain to relax and let go. Since most plasticines don’t dry out, you can keep the other attempts for next time.
Don’t forget scale models, too. Make your small version as a guide.
No matter which medium you prefer, go have some fun.