Everyone is going to speak to their favorite brand.
Each brand had: entry level, middle level, and high end for the most part.
Note that some/most of the mechanical parts that get a bike together were either very similar or the same brand.
Like most bikes use ND rear ends, or the same bearings and handlebars. Even pedals were exactly the same or just a More deluxe version. At the end of the day it all about the mechanical adjusting it correctly.
So then the next thing leaves you with, is which brand had the best geometry and materials that work for you.
Then the next thing is finding the designs that you like.
Last note, if you are collecting or futureproofing your investment. Just find the best version of popular models the get bought and sold frequently here. Odd balls have to be very rare and special and in demand.
Treat it like you are buying a hot rod or classic cars, common ones in the best original condition will most likely sell and get you money back. Like ‘32 Fords and ‘57 Chevies.
If you don’t want to go down the rabbit hole of collecting here. Buy one nice bike you would like to own and ride for a while.
Then save a lot of money and buy the best version of your dream collector bike. You don’t need everything else in between. It is just a waste of space,time and money. That is if you never use it for what it is, at least a bike.
That is why most of these guys, including me are buying and selling here and there. We need to move things, to buy things.
For me, I’m pretty much done. Just cleaning up and making a small focused couple bikes to keep and ride and get over it. If you try keep with the trends here you end up buying a bunch of stuff you don’t need. Who the hell needs 2-3 bedrooms full of bikes, not me.
Good luck.