I have been looking at the same type of aircraft for a few months now. I was first interested in the Challenger II, but I've heard some negative comments about roll authority with the flapperons. They don't have ailerons, but have a full span flap, that deploys independently to try rolling the plane. Apparently this produces a lot of adverse yaw, and the plane is controlled in roll more by the rudder. The vertical stabilizer has a mod for some big tabs mounted outboard of the elevator arm. They are supposed to be on every Challenger that has floats, although I've seen some without.
I'm now looking at the Buccaneer II amphib, but it also has a weakness, although not as bad. The gear legs don't take a lot of side force, and quite a number have broken, leading to a short ground-loop. Since there's a sponson outboard and below the strut brace, the wing isn't usually damaged, but the sponson, and part of the hull scrape, requiring repair.
The Eipper Quicksilver MX series are good planes in general. They've been around since the beginning and have fixed a lot of the early gaffes by now. It is a wire braced wing and the failure of any one wire could bring it down. I would recommend the later offerings like the Sport or GT models, which are strut braced, and a bit more costly.
The top of the line, start to get very expensive. I'm trying to stay under about $15k for one, and that's become a challenge to find one that's in decent condition, with good sails. Usually, every used one I've seen is going to need sails immediately, to a year, and that's about $3500 or so depending on model.
