Texas:

Getting back to your original question, I chose a Hangar 9 T-34 Mentor for my second plane. I've flown it twice so far, and the biggest difference is that it's more reactive to control input, especially aileron (first impression was that it was really twitchy, with lots of accidental knife-edge flight!). You also have to keep the speed up, not full throttle all the time, but by adding a couple of clicks before you enter a turn to help with stability. Take-offs are also different, it needs a bit more ground speed to get into the air, translating into a longer take-off roll. Landing, it won't float in, with the T-34 you've got to fly it all the way to the ground at a reasonable speed and land it "hotter" than a trainer.

Is it the easiest 2nd plane? Probably not. But it's an idea.