Welcome to this extraordinarily knowledgeable and generous community. Never any question too simple nor too esoteric.
I have and use all four of the pens you are considering. Of the four, the Pilot just seems to find itself in use more than the others. If you want a "pick one" recommendation amongst them, I'd recommend the Pilot. Lots of joy. No regrets.
Now some nuance:
While I haven't looked up the numbers nor hauled out all four pens just now, my recollection is that there's a pretty mighty difference in mass (or, if you prefer, weight) between your four choices. The Karas is built like a tank, which is its charm and its sin. After a few pages, it can feel like you're pushing an armoured vehicle across the page. Your writing habits and mine may differ, but I find the Karas tests my patience and stamina in long sessions.
My Carene writes like a dream, but (1) there's no particular character to the nib, and (2) the lacquer has chipped without particularly rough handling -- which isn't uncommon, anecdotally. It's also got some weight to it.
Some folks suggest that the Japanese nibs are utilitarian and lacking in character, too. That's not been my (qualitative, inductive, personal) experience of Japanese gold nibs. I find they can be quite a bit more suggestive/expressive than mass-produced steel nails. They don't have big personalities, but I think they bring subtle interest and intrigue. And, as has already been covered in this thread, you have quite a bit of nib choice with the Pilot.
(And that would be my personally held exception to the sound view that neither steel nor gold is a superior nib material. I agree with the generalism, entirely. Much more depends on the specifics of an individual nib than depends on its material, per se. But I find Japanese steel nibs pretty undifferentiated and generic -- however stunningly reliable -- while Japanese gold nibs do bring some subtle character to the party. And the Japanese definitely offer range.)
As for the Falcon: Great pen. But, for me, it's a specialty nib. It certainly *could* be a daily workhorse, but that remit suggests an "all rounder", whereas the Falcon is a delightful specialist. I wouldn't choose it as your one-and-only unless you'd had the opportunity to write with one and found it to be the undeniable Bacall to your Bogart.
I agree with those who suggest that, if you like the Pilot, you might enjoy agonising over a comparison with Sailor. Both are outstanding. Can't go wrong with either.
Whatever you choose, I highly recommend that the moment you purchase it, you hold it aloft and declare that you made the perfect decision, and never look back. Then write your tuchas off.
Have fun out there.