Aside from the obvious differences in cost, build time and seats:
* The -10 is like a full sized airplane, the -14 is a traditional RV size. With my surgically repaired spine, the -10 is substantially harder to push on the ramp than the -14.
* The -10 has a baggage door.
* The -10 is often at the forward end of the c.g. That motivates carrying emergency and semi-emergency stuff in the baggage compartment all the time -- water, some survival gear, small tool box, spare nuts and bolts, etc. And you can carry all that (within reason) while still carrying a load of baggage, especially with the back seats empty.
* If I still had a dog, the -10 would work but the -14 would be awkward.
In an ideal world, I'd have a -10 with some kind of portable powered tow bar.
In the real world, the RV-9A has turned out to be exactly the right plane for developing the Expanded Envelope Exercises®. (Shameless hint: looking for low time pilots to come to Savannah to fly with me and fly the Exercises. We could turn that into a Flight Review, also.)
Ed