Desert Island: ship has sunk. I only rescued one pen. No idea when I'll get Wifi back to order another one.
I'd have to say M205. For personal reasons, partly: my first love was an M100 in the 80s which travelled everywhere with me. I also think it's a fun pen - more fun than the 2000. I'm currently using the M205 demo and it feels like a Mazda Miata, small, sporty, close to the page. Absolutely uncomplicated and the steel nib, while not luxe, is as good as everybody says it is - springy, versatile, game.
My tale is very similar to yours, including the "first experience" with the model being an M100 (early ninties, in my case).
Main difference would be that, given the choice, I'd get an M215 instead of M200 model (I feel the extra weight, albeit minimal, makes for quite a different experience), and then, with a 1951-54 "plain" gold nib instead of the model's steel one (well, in fact, I have inked just such combination right now).
But if I couldn't get the old gold nib, my second choice would be the steel nib in preference over the M400 gold one.