I have 14 bikes, and my wife and two sons count for another 6.
I live in Mexico where opportunities for flipping are very limited, so anything I buy is with the idea that it’s a keeper. I collect for enjoyment and not with the idea of an investment, so I don’t care what any of my stuff is worth. The one bike I won’t sell is the Grand Jubile, for sentimental reasons.
All my bikes share a few characteristics:
First, they are all riders, so they have to fit and be in good functional condition. They must also match my type of riding, which consists mostly of recreational riding on paved roads and urban commuting.
They must look good (to me anyway).
Nearly all are high-end lightweights (for their category and time period).
Beyond that, I aim for a variety of nationalities, eras, and types—of frames as well as components.
Nationality: mostly European, especially English, French, and Italian. My newer bikes are American. No Japanese yet, but you never know.
Eras: It was 60’s-80’s, but I’ve been extending it back to the 40’s. I have one 90’s carbon fiber racer, just to see what all the fuss is about and to avoid being too much of a retro-grouch.
Types: Mostly racing and sport touring bikes for recreational excursions. I have a couple older MTB’s which are my beater utilitarians for commuting, gravel, and touring.
Grails: No particular makes or models, I like surprises. Someday I’m gonna get me a nice constructeur-built French bike.
I am not a cheapskate, but I usually try to avoid paying a big premium for a famous name. I’d rather get something I’ve never heard of before that not everybody else has.
Recent tendencies: I’ve been passing my mass-produced factory bikes to my sons and replacing them with artisan-built frames from small shops. I’ve also been getting into older bikes from the 40’s and 50’s.

Mine:
48 Stallard Malvern—SS fixed/free racer
49 Automoto—city bike
50 Rotrax Super Course—3sp club rider
62 Jack Taylor International—sport tourer
67 Atala Record—racer
68 Lejeune (Professional?)—racer
73 RIH Model Campagnolo—sport tourer
75 Motobecane Grand Jubile—650B sport tourer
82 Messina Specialissima (Villata)—racer
84 Brazzo La Certosina (Losa)—racer
86 Davidson Discovery—sport tourer
88 Fisher Ascent—MTB/tourer
89 Diamondback Apex—MTB/tourer
95 Kestrel 200—racer

Family:
72 Motobecane Le Champion
74 Raleigh International
91 Klein Kirsten
92 Trek 520
95 Trek 6500
99 Klein Attitude