Early on I was seriously considering the Sonex. I was also considering a Van's RV-6/7. Here's the things that made me decide to go with the RV (I'm building an RV-6 now).
The Sonex looked pretty affordable at first but when I looked closer the $ gap between it and the RV started to close up. For example, there is a $2k premium on the Sonex if the various sub-assembly kits are not all purchased at the same time. Then there are quite a few pieces that need to be machined or can be purchased from Sonex, once again at an additional cost.
Suddenly the kit wasn't so inexpensive. In fact if I were to purchased the kit one subassembly at a time (which is the only way that I could afford to do so) the cost of the basic airframes were not all that far apart.
Then there was performance. Essentially, the RV is a pretty solid 40-50 miles an hour faster than the Sonex. That's not insignificant. On the other hand the Sonex does go much farther on a drop of gas, which is a good thing.
I was somewhat concerned about the long term durability of the VW engine. The Jab seems to be a fine piece of engineering but again I could get a nice mid hour Lycoming for the cost of the Jab.
Essentially, I expected to pay a bit more for an RV but not THAT much more and I expected to get a lot more airplane (and more shoulder room).
So how did it work out?
Well, I kept my eyes opened and found myself a RV-6A fusalage, wing and and two emp kits all for $6500. A few pieces are missing but not many. So I've already done a lot of catch up on the low price of a Sonex. Who knows, if I find the right prices on an engine I might even be able to put my RV together for somewhere around the $25k that Sonex says their Aero-V model can be built for.
Having said all that, I will also say that the Sonex appears to be a pretty neat little airplane and I did give it serious consideration. But I decided to take a different route for the reasons I explained.