I've played as Olimar, and I have to say, he plays like 3 of my favorite characters from Melee. Here's who I'd recommend.
Peach: proficiency w/ projectiles - getting their trajectory down, being able to quickly recognize the properties of the one you'll throw next, but generally not relying on your ranged attacks for kills - only for harassing and increasing damage.
Pikachu: short, fast, throws himself at opponents (i.e. non-Pikmin attacks) and has some surprisingly long disjointed hitboxes. Also, interesting projectiles (ground thundershock, air thundershock, chasing combo'd opponents with a thunder, reversing your thundershock, etc) that can be a huge advantage if you know their ins and outs. Has a sort of guerilla warfare type playstyle - you rack up the damage with small annoying hits and combo when safe rather than beefy attacks.
Ice Climbers: technical skill, intense situational awareness - The Ice Climbers are (in my opinion) one of the hardest characters to master in SSBM, simply because there is so much you have to be aware of at one point in time! Olimar seems like he'll be the new IC's, because of how many factors you have to consider when playing him. How many Pikmin do I have? What is their order and what colors? For each attack, it's best to know what type of Pikmin will be used, so you can follow up with a better combo. Olimar's unpredictability is a huge disadvantage to opponents, but can be a disadvantage to players unless you know exactly what your next attacks properties will be.
Marth: Spacing game, ranged F-smash - as much as I don't like it, Olimar can also play sort of like MarFALCON PUNCH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!