I’m not sure special is the word I’d use, all my bikes are right for me, they provide that feeling when out on a ride that all the stars have aligned and the riding seems as good as it gets, or even the mundane getting home without some nagging thought that it could have been better. I don’t feel this all the time, but often enough to know it’s not the bike when I don’t. Getting there has involved some trial and error, a few bikes and components that didn’t work out, learning not just abut the bike but also my cycling – I had three good Audax bikes over a period of fifteen years, before realising I wasn’t riding them in a way where I was benefitting from their main attributes – I could say I now have a good idea about what I need to be comfortable, though it might be more accurate to say I’ve learnt some things to avoid. The bikes handle the way I expect them to, I’ve rejected steering geometries that seemed to twitchy or ponderous, though some of that might be familiarity. I’ve found components that work for me… I know it all… except I don’t know much at all.
It’s like when you go for an eye test and they put a lens in and everything looks crystal clear, then they put another in and it looks even better, then another and another, till there’s nothing left that can improve it… With bikes, unless you have unlimited time and resources, you’ll stop looking when it feels good, you’ll never know if that’s the best, just that it’s the best you know and you can be happy with it. I’ve rejected the things that haven’t worked for me, or have felt that about. I don’t know more than that, it’s both easy and dangerous to think those anecdotes constitute enough data to be sure of any conclusion. You prefer bike B to bike A, maybe there’s a dozen differences between them, you think you know which are improvements, maybe you do, but unless you’re able to try every permutation you don’t know. Maybe you even started with an idea and as Moronic says the result is influenced by confirmation bias. It doesn’t matter, as Dan says at the top of this thread “If you find a bike you like -- even love -- simply keep and enjoy it and love it to pieces!”
A story to illustrate the point – I ride with someone who’ll tell you that lugged steel frames are the most comfortable. He’s had lots of bikes and the common denominator of those he’s found comfortable is that they’ve all been lugged steel. He’s not interested in having any other differences pointed out, oversize tubing, compact frames, the different frame material… It’s entirely his business what he prefers, but he insists on telling every new club rider that’s what they should have.
Then, even with your limited data, there’s the minefield of interpretation. I have two Mercurys, my best bike, Rohloff, dynamo lighting, mudguards… and my original crashed/repaired one, heavier fork, no dynamo or guards, Alfine 8 gears, slightly chunkier tyres. My rides on the Alfine one have been faster, I have the data. So, it’s a faster bike? No, the lack of low gears means it doesn’t go into the Peak District, the lack of lights and guards means it rarely goes out in the rain or after dark, because it’s less precious to me I might ride it with a bit less respect… OK, I’ve made those differences obvious, but sometimes there’s subtle ones that if you’re not careful can lead to false impressions.
Then there's aesthetics, I know bikes are for riding and the look doesn't alter that, but we are vain, well I am, I'll like a bike more if it looks right.
Special for me is the cycling, the right bike is one that doesn't detract from it.
EDIT – Just for fun my bike list, in order of mileage, highest first
Surly Ogre, Rohloff, dynamo, mudguards, rack - My most used bike, utility, light off-road, full-on camping. 29er 2” Almotion tyres.
Mercury Rohloff, dynamo, mudguards, rack - fun rides, Audax, lighter touring, social club runs. 700c, 40mm Supreme tyres
Mercury Alfine, no dynamo or guards, rack. - Still finding it’s place in the stable, might get more utility use in place of the Ogre in the summer. 700c 40mm Almotion tyres
Airnimal Folder, Rohloff, optional rack and guards, also a matching trailer. - My travel bike, any touring that includes considerable non cycling travel, this is the bike I’ll use. 24” 1.75 Marathon tyres
Hewitt Cheviot SE, quite traditional tourer, derailleur and drop bars. - Somewhat superseded by the Mercury, currently built up quite light, no rack or guards, will use it on sunny club runs and shorter Audax. 700c 35mm Supreme tyres
Brompton B75, the most basic model though I added guards and a rack. Bought specifically for some work that involved rush hour train travel, I’m a fan of the fold, but I’m unlikely to ever ride it further than necessary. 16” and standard tyres?
If for some reason I had to start afresh, I'd replace the Mercury, Ogre and Joey like for like, but wouldn't bother with the 2nd Mercury or Hewitt, simply because they add nothing that the others couldn't cover. I'd replace the Brompton if and when I had a use for it.
Also, for work I have an E-bike, a Trek Allant+ 5 with a Bosch Performance CX motor and two batteries. 650B, 60mm tyres. Last year it did more mileage than all the others combined, but it’s only used for delivery work. I haven’t done any other riding on it though I keep saying I might. I does the job and it’s sometimes fun to power up the hills that I would otherwise struggle on, but I have no love for it.