What's the single best bike you've ever owned & why?

[PhilipV]

For me it’s a toss up between my “current” hard tail, a 2006 On-One 456, and my previous trail bike, a 2016 Giant Trance 2 (27.5.)
 

The On One is one of the bikes I dreamed about as a school laaitjie, and is still serious fun to ride. It’s done big day out rides, bike packing, faffing around in mud, pump track rides, jump trails and is now on SS guise, reminding me why I love bikes every time I ride it. It was slapped together as hand-me-down parts from the trail bike and 2nd hand bargains I hunted. 
 

But the Trance is the bike that opened big mountains, gnarly enduro and allowed me to explore my love of rocks. It showed me what side of riding I love I love most, and showed me how fast I can really be. I even rode it on long gravel roads just for the sake of riding, because riding is lekker.
I replaced everything but the front brake and the crank over its 5 year lifespan.

And I was genuinely sad when I broke that (the second) frame and retired it for a 29er. The replacement (Scott Genius) is a better bike in all aspects, but the Trance will always have a soft spot in my heart. 

[Dirt Tracker]

2016 Transition Smuggler without a doubt. 
Sold it to get a Commencal Meta
Sold it to get a Evil Following
Sold it to get a Evil Offering
Sold it to get a Orange Stage 6 and Dee Dar
Sold them to get a Canyon something
Sold it to get a Kingdom Vendetta (nearly the best bike of all time)
Sold it to get a Ibis Ripmo
Sold it to get Ripmo V2
Sold it to build a monster gravel bike
Sold it to buy more surfboards
Didn't sell any surfboards but bought a Shand Shug
Sold it and bought a 2017 Smuggler frame and built it as a Super fun trail rail'r.
Don't think I'll sell it and might only replace out with a new Smuggler or a Ti Chromag.

Why? Because even though it's 115mm rear and 140mm up front it'll take on anything that any of those other bikes will take on and do it with more capable goofyness than all the rest. Was Downcountry before that was a thing. Fun, playful, responsive and after going through the other bikes it still suits most of SA trails the best. Don't live on the north shore, very few trails here are needing super slack, monster travel rigs. Still holds the PR's on everything from Tokai to Jonkers.