My first three picks were Rayman, Snake, and King K. Rool, as they are my top three. I also picked the other veterans (Wolf, Lucas, Ice Climbers) Dixie Kong, and Lip. I do want to see them, but not so much as the first three. Thoughts on my choices:
Rayman: Currently, he has a trophy in the Wii U version. This is out of place, as he's a third party character, the trouble with which to go through licensing would be better used for an actual playable character, rather than a tiny cameo. As Mewtwo has shown, characters who are already in the game as trophies, but aren't playable can be made into DLC and added to the game. Rayman is an optimal choice, as they already have the rights for him in the game, and he's the mascot of Ubisoft.
Snake: A lost veteran from Brawl, also a third party character. We know that Kojima still wants Snake in, as he's said "please use Snake." The trouble that Sakurai went through to include Snake in Brawl, when he was originally wanted in Melee, should speak a lot about how Sakurai feels about the character/franchise. As with Mewtwo, Snake is a largely popular character with a completely unique moveset, compared to the other cuts (besides the Ice Climbers), but he lacks any sort of trophy appearance currently.
King K. Rool: Having consistently been among the top three most requested characters after Mega Man joined, with Mewtwo out of the way and Ridley being down for the count, K. Rool has inherited the largest amount of support for Smash currently. While he could potentially be looked over due to his lack of appearances in the past few years, he is still recognized by Smash itself with a trophy appearance, likening him to Bowser as the main villain of Donkey Kong, no less. The CEO of Retro has also recently followed the Twitter account, Kremling Kampaign, which aims to bring the King back to the DK franchise and add him to Smash.
Ice Climbers: Though they seem to have been put on ice, there is still the possibility of Sakurai managing to fix them eventually. This would require more work and effort than he already put into them, as they were working on the Wii U but ultimately scrapped, so their lower priority could hinder them. Never the less, they are a fan favorite veteran that we want back.
Wolf: One of the cuts that baffles me almost as much as the Climbers, a perfectly unique veteran, a villainous character, and fan favorite that should have been in the game. He almost feels like the Mewtwo of Brawl, in that respect. But again, with Mewtwo coming back, Wolf should have no problems making his way to the DLC train, with his high support.
Lucas: One of the more saddening cuts, this poor kid can never get a break. Another unique character, though from a Japan only game, it's one that has gained it's own following over the years, as evidenced by Lucas having by far the largest fan outcry of any of the cut veterans. At least Lucas has a better chance of returning than Mother 3 has of being localized, right?
Dixie Kong: One of the infamous characters of the "forbidden seven," this Kong was planned to be in Brawl, but plans fell through. With Donkey Kong getting no characters whatsoever with this iteration of Smash, and being at a measly two characters when it has such a large plethora of them to work with, it would be more than justified for there to be two, or even three DLC characters from the franchise. Dixie is one of the original protagonists of the classic trilogy, starring in two of the games (two more than Donkey Kong himself!), and having a grand return in Tropical Freeze, she's a perfect candidate to become playable.
If only we could have the Kremling and the Kong...
Lip: The puzzling fairy that got lost in translation, original protagonist of Panel de Pon, before it was turned into a Yoshi game with the generic title of "Tetris Attack," and then turned into a Pokemon Puzzle game, before ultimately becoming a generic puzzle league game with no characterization, even in the original Japanese versions. Lip herself hasn't been forgotten entirely, still making small cameos in her own games, and her magic flower wand being an item in Smash (plus one of Kirby's Stone transformations being a Garbage Block), so there's the smallest glimmer of hope for her to return in some way.