FWIW - I too keep looking at the options (including finishing my 9). I built a spreadsheet, looked at the data and talked with some folks that have real experience building and or supplying those models - Jabiru USA. As my odometer gets more gray I start thinking more about the LSA world.
I just like the idea of a Jabiru over the Rotax. The price is better, the engine looks like a work of art, cheaper to overhaul, etc. Jabiru USA has built the S-19 & is currently building the RV-12, they've put their stuff in the Sonex and the Zenith. A couple of their employees are RV-6 builders, at least one a Zenith and others thrown into the mix as well. Call them and talk to them to get a different perspective. You may not agree based upon your needs but its always great to get a perspective from someone that has been there and done that. They may not recommend but they may tell you about thier experiences.
The Sonex in a sense is really in a different class. Only 1100 punds gross (with the Aero-Vee - which is 80 horsepower). The Jabiru 3300 bumps the gross up to 1150. The RV-12, Zenith and S-19 gross weight is 1320 (LSA). The Sonex has a cockpit width of 40 at the sholders and 38 at the hips. The RV-12 & the rest are 43 - 44 inches wide. The Sonex can do mild aerobatics (not a big deal for me since I consider thermals aerobatic enough). The Sonex may also work best as a roomy single passenger (at least at my grossest weight), although I think I could get it to meet even the needs of including a passenger (barely - as long as my tooth brush was carbon fiber)...if only I could get 100 pounds more gross weight out of that...
Basically the Sonex (regardless of the engine used) is a little smaller plane than the others. It is aerobatic, the Aero-Vee is
really inexpensive and they even have a turbo getting ready as an add on (rumored at about 2K). The kit only has a few of the parts (skins) pre-drilled compared to the RV's and unless you get the machined kit parts there's a lot of bending, sawing, hammering & rivet line layouts & drilling to do.
The Rans S-19, RV-12 & Zenith are really a little larger and you may want to think of them in that grouping. They have bigger payload (although the S-19 is a little light on useful load in the LSA config) & larger cockpits.
What really makes the Sonex less expensive is the Aero-Vee (or even the Revmaster) and you are forced to have very little in your panel since your panel is very little. I took a video last year of a local Sonex being built. You'll see my hand laid up against the panel - its a normal sized hand...
http://www.vimeo.com/12303046. The Sonex has simple brakes operated by a lever. The plane is simple in concept (I mean that in a good way) which also means simple to maintain and a litttle cheaper to build.
The Sonex kit (if you add the machined parts, pre-made wing spars and dual stick options) is a little more than 18K & the RV-12 is a little more than 21k. It's the Rotax and panel that bump up the price of the 12. The S-19 kit will typically come in around 25K.
Less dollars but longer build times and a bit smaller plane the Sonex might win based upon that criteria. I like the rotationally pre-made tank but it only holds 16 gallons. I'd like a little more on the gross weight and living in high altitude enivronments more power than the Aero-Vee can currently put out (maybe the turbo would help or the Jabiru).
Ease of build is hands down won by the 12, the opposite end of the scale from what I've been able to find out is the Sonex, with the Zenith and Rans falling in between. Nothing extra to buy on the 12 is certainly appealing, user support from the factory is good on them all and even web support is good on most (of course all the flying RV's and this forum is a huge plus). Sonex has a Yahoo group (I would miss the organization of these forums).
Just to throw another wrench into the picture Dave Thatcher is working on a two place CX-5 follow on to his popular CX-4. Both run VW's.
Check out the asking prices on Barnstomers for the various models you're looking at.
Whatever you build flying is almost always better than driving (which is what I'm stuck doing)!
Bob