The 4* .60 if you can swing it. It's still easy to build, so you're chances of sucess is better.
You can frame it in an weekend. The .60 is easier to build than the .40 in many ways.
The kits are also lazor cut today, so the parts are cleaner and less sanding.
The hardest part is beveling the control surfaces.

I personally think a second model should be a kit. Not only is the 4* easy to build, it's also easy to repair.