Hm, I've always sort of rated the characters on the terms "ease of use" and "advancement potential". Kirby, in my opinion, is one of the easiest characters to use, and a good choice for beginners. But the potential isn't there; he just can't cut it when you try to play him seriously. This has been true in both games.
As for the differences between the games... I appreciate SSB for what it was and what it began, but SSBM is just superior in nearly every way. I'd played SSB again recently, and in comparison it's just so slow, the movements are much more constricted, the characters are much more imbalanced (not to mention the items)... There are certainly things that I've missed from the original, but Melee is just such an improvement; there's no going back.