The Fenix P1 is the smallest of my CR123 lights by only a mm or two. The pocket body FireFly would be smaller, but I only have the keychain body. The Jet-1 is about the same as the FF, but several protected rechargeable batteries will not fit in it, where the P1 will probably fit anything because of it's larger battery bay.
Though I like the exterior design of the P1 as more rounded and asthetically pleasing in an organic way, the Jet-1 will satisfy those looking for a more harder industrial look. The P1 is smoother in the pocket because of more rounded tail design. Irrespective of that, I happened to have won the Luxeon lottery on my Jet, but got a more purple-ish tint in my P1. My Jet-1 on Li-Ion is very bright (and white), but still not as bright (or white) as my HDS EDC B60, so neither the Jet or P1 are hitting 60 Lumens they aspire to. I'd guess 50-55 for the Jet-1 and 40-50 for the P1. The FireFly3 is supposed to be right around 60 Lumens, so it should beat both the more simple contenders.
The Exolion is a CR2 light.