The Simple Scout is a durable, stable flying airplane, though as a trainer, its size and ability to roll quickly can be a detriment. I have reduced rates and expo on mine, and it'll still roll over faster than a member of congress for a deep-pockets lobbyist. That said, I've also been flying mine for over two and a half years, and it's still one of my "go-to" planes that almost always makes the trip out to the flying field. My first couple of flights with the Scout almost went bad at take-off, as that narrow wingspan can make it very susceptible to torque roll on lift-off. Once I figured out that it will take off just fine at about half-throttle or so, my take offs became far more stable and less stressful. The Scout was my first Flite Test build, as I bought the SBK from a hobby shop on a whim. When it finally either wears out or I finally crash it, I'll build another without hesitation. I'm sure I have well over 100 flights on mine now.
The Storch would be a decent trainer. Its size makes it fairly easy to see in the air. It takes off and lands at a very slow speed, is pretty stable in flight, and is one of the easiest to land planes I own. Its wingspan makes for a very sedate roll rate, without leaving it feeling unresponsive to control inputs. It's not really a good plane for learning aerobatics, but for the basics, it's just an all-around nice plane.
The Bushwacker is, IMNSHO, a bit better as a step-up plane. Its wing, both in span and that it's a flat wing, make for a more aerobatic plane. It will roll and loop tightly, which for a beginner, can often spell disaster when the plane responds too quickly, and the novice is trying to think of what to do to recover properly. It's a fun to fly plane, though, and quite capable, when you get the right amount of weight up front for proper CG.
The Explorer also makes for a decent trainer, with the design easily accommodating either 3 or 4 channel control. It's large enough for easy visibility in the sky, fairly stable and sedate on controls, and like the Storch, will fly at a fairly slow speed. It's also a reasonably simple design to build.
I enjoy flying the Tiny Trainer as well, though it's another that I'm not sure I would have done well with as a first trainer plane. I've only flown with the 4 channel sport wing, though, so I can't say how it would be on the 3 channel polyhedral wing.
