I think it is fair to say that the Zeiss Conquest is the smallest and lightest, and the Nikon is the largest and heaviest. The Leica Ultravid, Leica Trinovid, Zeiss Victory, and Swarovski models are all intermediate in size and weight, and the differences among them are not significant. Note that the Leica are available in rubber armored and in leather/faux leather versions; the latter are both slightly more compact and somewhat lighter in weight.
For me, the goal for a small bino is to be as small, lightweight, and unfiddly as possible. Being light is as important as being small because it effects how securely the bin must be stowed while hiking and messing with other equipment. When hiking, I like to wear my 8x20 Zeiss Victory or Leica Ultravid (leather/faux leather version) on a neck cord. I then tuck the bin in a large front shirt pocket, or, if I'm wearing a backpack I hook the end of one barrel into an elastic band affixed to one of the backpack straps at chest height, or to the "sternum strap" of the backpack. In that position, it is available at a moment's notice but is otherwise out of the way.
I like the Zeiss Victory and Leica Ultravid leather version equally well for their very small (essentially identical) size and light weight (and their superb optics, long eye relief, and very close focus). Both hang flat. Both are easy to set up quickly because the Zeiss has a single hinge and the Leica Ultravid has positive stops in its hinges such that one side can be immediately unfolded all the way before even looking through the bin, then the other side unfolded in similar fashion as the single hinge on the Zeiss to set the IPD. Those who like to hold their bin in their left hand and/or focus with their left hand may not like the right hand bias of the Zeiss Victory.
I'm not a fan of the Zeiss Conquest; it has inferior optics, is very fiddly due to lack of positive stops in the hinges, a poor neckstrap design (doesn't attach/hang well, can't be replaced easily), and it just doesn't seem as fine a product as any of the other choices.
I own, and have heavily used two generations of the B&L 7x26 Custom Compact. It is a fine bin, but I find it does not perform as well as the others against the light, and it is considerably more bulky. If I want something bigger than 8x20, I go to a small 8x32.
--AP