I suppose I now have time to give my reasons and opinions on who I chose and why, so here it is:
Miles "Tails" Prower - In Tails' case, the reason I chose him was because I thought if anyone should appear in Smash alongside Sonic, who better than his best friend? Tails also has the most recognition alongside Sonic ever since 1992, being the Luigi to Sonic's Mario. If he was in, I'd have no complaints.
Arle Nadja and Carbuncle - Arle is another SEGA character I would LOVE to see join Smash sometime soon. For one thing, her games, Puyo Puyo (Puyo Pop in other regions of the world outside of Japan) is a massively popular series and I love the story-telling. It's simple and it's pretty hilarious. Also, at the moment, as far as I know, Puyo Puyo currently keeps releasing NEW games every 2-3 years, which is unfortunately more than than other SEGA series (that are NOT Sonic) have done in a while. Also, I'm just a big Arle and Carbuncle fan. Heck, they're literally the ONLY 3rd party character I voted for on the official Smash Ballot. (With the suggestion of the other two Puyo protagonists, Amitie and Ringo, as alt. skins for Arle, in the vein of Captain Olimar and Alph, or Bowser Jr. and the Koopalings.) This is what I put down as the reason for them in the Smash Ballot.
"Arle Nadja is a SEGA character who has a MASSIVE legacy and fanbase behind her. Just as big as Sonic the Hedgehog, as a matter of fact. She is known for the Puyo Pop series and from her series, she could use her various spells, Fire, Ice Storm, Thunder, Diacute, Heavenly Ray and Bayoeen as magical spells to defend herself. She can also use the Puyo themselves to protect her from incoming attacks. She could also have Amitie (from Puyo Pop Fever) and Ringo Andou (from Puyo Puyo 7) as alternate skins like Alph. Her rabbit-like pet Carbuncle, could act similar to Luma and fight alongside her."
Opa Opa - I'll be honest, I don't know TOO much about Fantasy Zone, except that Opa Opa is the main protagonist of the series, and could be considered as SEGA's first "mascot". But hey, the idea of a sentient mini-spaceship seems pretty darn interesting to me.
Billy Hatcher - After seeing some gameplay, I'd have to say that Billy is someone that I think would a good second SEGA rep for Smash. After seeing his game and the gameplay in it, Billy could use various colored eggs in different ways, rolling them into his opponents or using their various elemental powers to fight with.
NiGHTS - Again, I don't know much about the series, but I feel that NiGHTS could be a decent choice as a second SEGA rep since it could use its dream powers and as a result, NiGHTS could be a very unique character in Smash.
AiAi - I've had a bit of an affinity for Super Monkey Ball, so AiAi could roll around in his little ball and move at high speeds, sending opponents flying and maybe borrow a few moves from Diddy Kong.
Amigo - By using dance, Amigo can use dance to confuse his opponents. Maybe some capioera thrown in the mix for him? His FS could pretty much be his SSF2 AT appearance as well.
I'll explain about Alex Kidd, Beat (Jet Set Radio) and Ryo Hazuki (Shenmue) later. I have to go somewhere. If you all have any better descriptions and reasonings about these characters, please tell me. I'll admit I'm not too well-versed in SEGA as I am in Nintendo, but SEGA is the one company I'd LOVE to see more (or at least 1-2 more) characters come from.