I do not know as of yet due to not knowing what the final roster will be or what changes will have been made to my characters, though I can say that Kirby will definitely be included... even if he sadly goes back to Melee levels (he does have the fireball charge; that does concern me).
I have found Ganondorf to be an enjoyable character to play as in both Brawl and SSB4, he even became my main in SSB4, so I'll likely include him. Meanwhile, I find myself really good with R.O.B. so he is a likely character. If I were just taking SSB4 into account, I'd next say Robin, but this game also includes the return of old mains of mine such as Pichu, Ice Climbers and Wolf. There are also newcomers that I'm interested in trying out such as Ridley, and to a lesser extent, Inkling.
For now though, I'd have my squad as this:
1) Kirby
2) Ganondorf
3) R.O.B.
4) Ice Climbers
5) Robin
If I were to include a different character, be it Wolf, Pichu, King Dedede (if he plays more like he did in Brawl, I found him better back then) or a newcomer such as Ridley, then the most likely character in the squad to go is from 5 upwards. Kirby, as my favourite video game character, is guaranteed a spot and Ganondorf is unlikely to go unless he feels drastically different.