My mains in smash 4 have been, pretty much from the beginning, Captain falcon and Bowser Jr (wendy specifically). To the original post this thread is about, I'd say that I've put bowser jr on the back burner for a while now, and in the past day or 2 I've begun to pick him back up as a secondary to Cfal (C fal takes a lot of work). Honestly, everyone saying bowser jr is garbage is sort of right, in that he's not roseluma, shiek, diddy or yoshi, and in that reguard most characters are sort of bad when you get right down to it. But just picking a character because they're good is really boring, and only a few people are going to be the best Diddy/roseluma/shiek/whatever, so just be the best Bowser Jr. you can be.
Don't play to win, play to have fun. That doesn't mean you can't be good, it just means you wont ruin the game by turning it into marvel vs capcom 3 (not to just hate on that game, mad respect for mvc players, but it really is just a tier-fest).
I think anyone who says a character can't be good is misunderstanding smash brothers entirely. It's not nearly about the character as much as it's about THE PLAYER!!! The person controlling the character! There are soooo many different levels of good super smash brothers players that one person who's really good could probably beat most of the other people in their city with any character at random. It's all about how much effort and practice you're willing to put into the game.
That being said, you should probably just pick who you feel comfortable with in the game. I used a lot of wario in brawl, and since I wasn't in love with the changes they made to him, I sort of dropped him too quickly. I mained c. Fal in melee, and since he sucked in brawl, I was really happy to see him buffed up a ton in smash 4. Right now I'm playing C fal as a main, with bowser jr as a secondary for my tougher matchups. I picked up bowser Jr because HE IS FUN! He has a lot of cool tricks, and his mindgames are insane, and like all matchups, you just have to understand your spacing/timing in relationship to your opponents, then read what they're going to do, and counter.
The game isn't about being the fastest, or knowing and using all the best combos, or making the most daring plays. Those are all nessesary and usefull components, but at it's core Super Smash Brothers has been and always will be about trying to understand your opponent, to accurately predict and counter what they're going to do. The idea that you can't have competitive and fun play to me is a popular misgnomer in my opinion, because many people blame their loss on "Oh, well, he just won because he's using character x". If you really want to enjoy this game AND get good, ignore the tier list, don't quit your character just because you're feeling down about him/her this day/week/month, and keep practicing! BOWSER JR FOR LYFE!!!!