The megaminx is a lot of fun to solve, because there's so much blockbuilding flexibility, and the whole solution is super-intuitive.
The Square One was the most fun puzzle to develop a solution for, but my solution (reduction to a 2x2 domino) isn't fast, and I have no desire to learn new algs for it, so I'm not that interested in solving it anymore.
The Square One was the most fun puzzle to develop a solution for, but my solution (reduction to a 2x2 domino) isn't fast, and I have no desire to learn new algs for it, so I'm not that interested in solving it anymore.