I used Marth for the first two days, then tried Ike, haven't looked back since.
My "secondaries" (AKA, whoever I used when bored) however, have bounced around as follows: Marth, Snake, Falcon (kept, but "knew" I needed a worth while secondary even though I don't bother using secondaries), Toon Link, Sheik, PT, Mario, G&W (only secondary I have attempted to use in a tournament. Went terrible), Toon Link again, Marth again, Sheik again, Bowser, Wario, D3, Bowser again, Link, Sheik again, Samus, Bowser again.
Those are the ones I used for more than a few days. Every other character in the game I have at least experimented with for a day, outside of Diddy Kong, ICs, Olimar and Jigglypuff who I all used for less than a day because I hated how they worked. If I really worked at Sheik, Charizard, and Bowser, I could probably get them on the same level as my Ike. I consider Falcon just one small step under my Ike's level. However, I see no point in attempting to learn any of them: I don't find them fun outside of Falcon, who isn't worthwhile to learn. I would consider Link worthwhile if he didn't fall like a rock incased in cement.
The only advantage to all of this is that I likely will have a leg up on most people when it comes to random character tournaments. :D