I've carried the Southard for months and I love the thing. It doesn't look like a classic Spyderco. It feels light, but burly at the same time. The Domino looks like the classic leaf-shaped blade Spyderco is known for. It may not quite be the hard use knife that the Southard is, but I think it will do just fine for most tasks. I think the Domino handle feels a little better in hand, but it's blade feels a bit dainty compared to the Southard.
I'm with nickites on this, his comparison is IMO on target. My favorite ZT flipper is the 0801, and I also have the Southard and Domino.
The 0801 flips incredibly well, looks great, and somehow feels even tankier to me than other ZTs. It's not huge, but it feels like a stout little monster. Locked, it feels like it never folded up in the first place. It's also bigger closed, heavy and thick, heavier and thicker than both the Southard and Domino by a large margin (e.g. it's over 50% heavier than my Southard, 3.8oz versus 5.8oz).
The Domino is the thinnest of the three, even compared to my slimmed down pimped Southard. It's almost as bulky as the ZT 0801, outside of being thinner and lighter. It feels quite a bit bigger in the pocket than the Southard, but around as big as the ZT 0801. It has a huge handle area when opened, thanks to the finger choil, but it also has a very small sharpened edge (about two thirds of an inch less than the Southard or ZT 0801). It flips just as well as the 0801--both feature feisty detents that make them fire perfectly every time.
The Southard is smaller closed than the other two, and almost as thin as the Domino (at least my slimmed down Southard is). Between being so much smaller, area-wise, closed and also being lighter, it feels much smaller in the pocket. It's super smooth, and flips very well, but not quite as well as the 0801 or Domino. It has the weird quality of feeling too light for its size, yet sturdy and reliable enough at the same time for anything that you want to throw at it. I find that handle very comfortable, and the depression in the smooth back of the spine make for a nice thumb spot for choking up. It's an amazing knife, one that I was completely uninterested in until someone I love bought me one (I always thought it was too fugly to buy, even if everyone loved it).
IMO, the Southard spanks the other two handily for carrying everywhere all the time. I love the 0801, but it's too heavy (to me) to carry in loose shorts or dress pants. For me, the Domino is an interesting novelty at best. It flips great, and I personally love the textured checked scale, but it's just a Sage with a flipper (=lots of handle, not so much sharp stuff).