That is one weird selection
To compare it to cars, it's a bit like asking if you should buy a minivan, hatchback or a saloon. These are very different things and whether their the right choice will depend on what you want to use them for.
It is indeed a bit odd so I've just done a bit of googling.
Trek District Carbon "all-carbon, dedicated singlespeed belt-drive bike". That's a bit niche.
Pinarello Paris, a carbon road bike - I noticed that it takes up to 30mm tyres
Canyon Aeroad 100% aero race bike. I noticed that it is incredibly ugly.
From that rather odd selection of bikes, the nearest thing that's an all-rounder for fitness is the Pinarello. It seems odd to be describing a Pinarello like that. The Trek District Carbon is a weird thing. The Aeroad is an all out aero race bike. If given the choice of them - say I happened to have won a raffle prize - I'd go for the Pinarello. But that's just me.
fitness / leg muscle building
Cycling tends not to build muscle. You need to go to the gym for that. Cycling is more about aerobic fitness.