I feel like they both served completely different functions, and both did it perfectly. For all my extreme bias for Conner (who is possibly my favorite DC character), I can't say he's "better" at being Superboy.
^^Btw every time I see someone calling for him to get a Nightwing treatment, my heart grows 3 sizes. He would do it perfectly, and it's so much better than being the Superman successor. By making his own way, he never has to be sitting on the bleachers for somebody to vacate a spot we all know is never truly going to be given up.