1. A proper road racing or road-sport bike - probably with a carbon or steel frame and ~Ultegra level components, such as this
or built on a frame like this
2. A city or hybrid or touring bike - probably with an IGH like a Rohloff or Alfine 11, randonneur or trekking bars, or something in the same vein
3. A 4-6" travel suspension MTB
4. A fat-tired snow bike.
5. A cargo trailer for use with #2 and likely #4
6. A rigid MTB, possibly single speed
I don't know what order I would get them in if I had no bike and not enough money to buy them all at once. I guess a good touring bike can go almost anywhere the others can go. ANd a trailer would mean I can do whatever I want with it.
A rigid and/or SS mtb would also be the cat's pyjamas, as these are super fun to ride, but you occaisionally just have to take your time... not so good for group road rides or loaded touring through the Hymalayas, but anything else.
I have owned the same road racing bike for the past ~20 years, and I avoided the tempatation to sell it because I knew it would take me a long time to get another. Even though it is the bike I use least out of my current stable (4 working bikes and a Chariot kid trailer that the kids have outgrown), I am glad I have it. If I was populating a new stable, this would likely be the third, as soon as I had a working MTB.
Then a suspension MTB to do more recreational riding.
Then a snow bike as they are a bit of a luxury, and I could turn the SS MTB into a studded-tire winter bike with little effort.