I also teach kit building once in a while, these days no one seems to want to bother learning so I only teach one person every year or two these days. Even a decade ago I would have a couple of students at a time and teach every month.
A lot depends on the piloting skills but I used to use the GP Super Sportster 60 then someone put me onto the Four Star by SIG so I started using there 60 size plane for older students and sometimes the 40 for younger people.
Older people can get there fingers into a bigger plane so that's one reason for the 60 4*. Older pilots can see a bigger plane easier, reason #2. The 60 doesn't do anything as fast as the 40 size so older students can handle it easier.
If the student is a better pilot then we remove a couple of wing bays in the 60 so it has a faster roll rate.
The 4* planes are very easy to build and very easy to fly. Landing and take off of the 4* 60 is great.
The one thing in the build I have forgotten once or twice is to install the shear web between the spars. I have built the plane so many times my brain sort of goes into neutral and I think I have forgotten that shear web twice. Not a big deal, I still install them.
Other then that I can't recall any building problem with the plane at all. Love the way SIG has you install the aileron servos.
Anyway, that has been my number one teaching kit over the years but as mentioned by prgonzalez the Up-Roar is the easiest kit for building. As a fun fly plane it was designed to be built over night and flown the next day. I love the plane but it may be a hand full for a lot of pilots. It is one of my all time favorites though and the Dazzler is close but a bit harder to build and fly.
There you have it, my two cents!!!