Personal anecdote in regards to the Atom.
Fell in love with it years ago after the infamous TG episode with Clarkson having his face destroyed. Soon after there was a local with one.
Ended up with a Caterham and couldn't be happier. There is now another local with a super fast limited edition Atom.
If I were to have a track only car, I'd probably chose the Atom for the same reasons I'm very happy as an owner of the Caterham. It just makes a better car, arguably a worse track weapon (legacy frame instead of new bottom up engineering, front engine instead of mid/rear, less Aero, less power etc)
However driving 7 on the street is a different ballgame. It feels much more compact (exterior and interior). You sit IN the Atom instead of feeling like you're wearing the car like the 7. Atom roll bars are high (shoulder level) and the interior is much more spacious. On the 7 you feel much more involved with the elements due to how the frame is designed. You can touch the ground as you're sitting in the car (can't do that in the Atom)
Comfort wise just a few features go a long way. Atom is essentially a motorcycle you drive feature wise. Cold? you get cold. Rain? you get wet (actually wetter and colder than a bike on which you at least have proper gear typically). Caterham is a transformer in regards to elements. Some Brits drive them year round, including winter (few crazies). Summer? No windshield, no doors (maybe half doors). A little colder or want highway? Put windshield on. Rain? Put a half hood on. Rain and cold? Half hood and doors and then turn on your heat. Etc. As far as storage, its laughably small but it's still more storage than Atom if you want to plan a long drive.