I'd go for a Brompton.

It has a great fold -- very small and clean. The chain is inside the fold, so you won't get chain grease all over. Narrow tires, some suspension, fenders, built-in rack, internal hub. Perfect choice for a multi-mode all-weather commute.

Airnimal doesn't fold, it just packs into a suitcase. So that's out.

Birdy is sportier but doesn't fold as well as a Brompton.

I know some folks like 'em, but IMO Dahon sucks. Lots of proprietary parts -- I can't even swap out the rear derailleur on my Mariner D7 -- and the handlepost is flexy so you can't pull back on the bars at all.