Tyler Callaway gave his thought on what would make a better Sonic Movie, but I have a better idea...
Back then, it was easier for a generation of kids without the money needed to buy a Genesis to get to know Sonic through the SATAM cartoon and the Archie Comics. During the era, we met the Freedom Fighters, led by the first female leader of a superhero team, Sally Acorn,
who led Sonic,
and on occasion, Antoine and Tails,
on missions to bring down the tyrannical traitor to her father's kingdom, the dictator of Robotropolis (formerly Mobotropolis), the pollution-loving and mechanical minded Julian Ivo Robotnik,
who-along his cowardly henchman, Snively and his robot soldiers, the Swatbots
-seek to turn the ENTIRE planet of Mobius, into a planet of metal, ruled only by the disgustingly obese madman. The franchise told that story through both sides and won my love, especially with the additions of Dulcy the Dragon, NICOLE, Knuckles the Echidna,
the Chaotic (all 4 of them), Juli-Su, Geoffrey St. John, Nack the Weasel, Ixis Naugus, Scourge the Hedgehog/Evil Sonic, Mammoth Mogul, Enerjak, and Scratch, Grounder & Coconuts.
But then the Sonic franchise went down the hill when it's producers brought back Amy and made her look like Sonic's main girlfriend (when in reality, Sally is his soulmate), then pointless (Big The Cat) and alluring (Rouge The Bat) characters began messing with certain formulas, like Sonic's main rivalry with Knuckles being replaced by Sonic's rivalry with Shadow, then SEGA decided to go 'kiddy' and made Sonic Heroes and Sonic X. Once they came into the picture, they then allowed the regular voice cast of the Sonic characters to be the weak cast hired by 4kids, who kept going with allowing themselves to permanently replace Robotnik's name with the crummy 'Eggman' name! Nowadays, characters like Metal Sonic and Shadow were only brought back for either a cameo or a repeat of defeats.
You want to make a good Sonic Movie?
A. Get the issues over with once and for all and talk Ken Penders, Archie Comics, and SEGA into an agreement and let them make a movie focused on teens, a movie like that can bring back fans old and new.
B. The story should NOT be a predictable 'good VS evil' plot, the games played to this day have already shown the 'what-if Sonic and Robotnik fought' scenario dozens of times. The story needs emotion, and can still kinda have a 'good vs evil' quality to it, but certain changes that evolve the characters' personality and maturity (including Sonic, who's never stopped acting like a smug asshole in the Dreamcast-Modern games, Sonic issue #248 and so-on) MUST be brought to light. Those and an important life lesson. And action/adventure, LOTS of action/adventure!
C. SEGA/Sonic Team's changes since Sonic Adventure must NOT be involved in the movie. That means...
1. No Egg-named robots OR the 'Eggman' name, restore Robotnik and his dark machines and dark taste, no colorful robots or hideouts.
2. No Amy focus, she steals attention form the main couple.
3. No new characters like Big, Rouge, Shadow, Cream, Chip, Orbot, Cubot, and so on.
4. No 4kids involvement whatsoever.
D. Robotnik is a great villain and all, he just shouldn't take the wheel in every movie (just in case a trilogy comes to mind). Give other Sonic villains a chance to shine, like Mammoth Mogul, Scourge and Naugus.
E. Character relationships! Keep Sonic & Sally as the main couple. Have them grow closer through the movie series until the last one, when they can live happily ever after. KEEP AMY AWAY! Have Sonic and Tails have an emotional bond of friendship. Have Sonic & Knuckles become the Batman VS Superman scenario. And make Sonic's enemies give him a challenge not only physically, but mentally.
F. Finally, you had some good choices for voice actors, but keep looking and keep choosing the best choice for each character, NO slip-ups or 'bomb-potential'. There, I just gave you an idea for the best Sonic movie(s) possible! I would strongly recommend following these steps, otherwise, nobody's going to win.