Second favourite, eh? Well... my first favourite would be Hoshi no Kirby, but I won't talk about that then.
My second favourite series (sheesh, these favourites lists are really hard to boil down more often than not) would be Kaze no Klonoa. I have played only the GBA titles but they are quite amusing - simplistic but entertaining when I don't need to indulge myself with so much story and dialogue (Klonoa Heroes had a ton of that, though...). I don't care much for the grade system in Dream Champ Tournament but everything else was just pure fun, and even in the second game I had trouble figuring out how to get past certain puzzles (even to the point of getting frustrated over it, but uh... I'll save that for later, jor).
Oh, and as for Sonic...? Give me a break; that strange thing isn't even on my top ten.