Both are excellent cameras. We actually expand our offerings in this group to include the popular Sony RX-100, Canon G-15 and a couple of others. Cameras are all similarly priced.
The advice to consider the housings and lens capabilities is good. We have a
Housing and Port Finder that might help.
The XZ-2 is a great camera, with a better lens, larger sensor and faster processor than the S110. It also has a flip out viewscreen for above water. The
Olympus PT-054 housing is an excellent OEM housing (much better than Canon's). The problem with it is that it has a long port and you have limited wide angle lenses available. We have found the new
Sea & Sea M67 Lens to work pretty well with it though.
Macro lenses are no problem and this is an excellent macro camera. The
XZ-2 is $100 off the next couple of weeks, btw. I have some shots taken with the XZ-1 (same lens and sensor) here.
The Canon S110 is a very good small camera and has a few housings available for it. Many people like the rich colors the Canon sensor produces. The
Nauticam NA-S110 is a great housing with all controls, aluminum construction and good ergonomics. You have more choices of W/A lenses, one of the best is the
Fix UWL-28 with about a 140 deg field of view.
Both cameras also have housings available from
Ikelite, which are sort of mid-range in size, capabilities and price.
We have lots of ready-to-go
compact housing systems on the website to give you a better overall idea.
Good luck!
Jack