I thought it was already established that those two stages are Sonic's best stages, so you always avoid going there.
I fought well against Sonic on Final Destination. Then I realized it was because of Smashladder. I suck at Smashville and I've had a Sonic almost beat me down on Town & City. Again, the latter online. Yet I don't see how the Animal Crossing stages help Ike any against Sonic or Diddy.
All things considered, Ike's best stages - in most cases - are Battlefield and Dream Land. Smashville is a straight-up neutral that seems to be better against facing Sonic than Final Destination does. In rare exceptions, characters such as Rosalina will kill us on BF/DL, while Sheik must NOT be taken to Smashville under any circumstance. Given those exceptions, right now our focus should be to establish several things:
1) Ike's worst matchups
2) Which stages to avoid.
3) Which stages to pick if BF/DL end up getting banned or stricken via Dave's Stupid Rule.
Ike's general bad matchups are Diddy, Sonic, Rosalina, Luigi, Meta-Knight, and Sheik. Other general high tiers, such as Captain Falcon, Mario, and Yoshi, tend to have a more even matchup against Ike, so stage picking isn't priority against them as you can beat them in most neutral settings. All of these listed options will be edited as users chime in.
Vs. Diddy
Bad stages - Lylat Cruise, Duck Hunt
Good stages - Smashville
*Do not ever take Diddy to Lylat Cruise. He can pressure you and simply keep you from landing the entire match. Don't forget the Banana Peel can cover one platform.
Vs. Sonic
Bad stages - Final Destination, Duck Hunt
Good stages - Smashville, Delfino Plaza
*Having watched Ryo beat StaticManny's Sonic on Smashville, the stage is at least practical. It's just well-known in the community that Sonic's best stage is FD.
**Notice that perhaps the most crucial weapon is Sonic's arsenal is his grab game. Kill-setups and long grab range are his bread and butter here. Taking Sonic to a platform-oriented stage takes out one of those options. If you land on a platform, he'll be forced to rely on Uair, Fair, and Nair. Nair only kills at 160% roughly, and Fair is only dangerous if he can get a juggle off the platform on Smashville or near the ledge for a three-juggle kill.
Vs. Rosalina & Luma
Bad stages - Battlefield, Dream Land, Delfino Plaza, Halberd, Town & City
Good stages - Smashville, Final Destination
*On Battlefield and Dream Land, she uses our own platform game against us. On Delfino Plaza and Halberd, she can go under the stage for free Uairs. She can also use the high platform of Delfino to score early kills with Uair juggles, just as she can on Town & City. Duck Hunt also seems fairly practical as her high kills are less reliable thanks to the high blast zone, and with smart play, she won't get you onto the tree for free juggles.
Vs. Luigi
Bad stages - Town & City, Delfino Plaza
Good stages - Duck Hunt
*His Luigi Cyclone is his most valuable kill move. Given Duck Hunt's high blast zone, it will take much longer for him to kill here. Learned while fighting Dandy Penguin at TFC.
Vs. Sheik
Bad stages - Smashville
Good stages - Delfino Plaza
*If it's not a given already, Sheik can kill you quickly using the platform for Fair combos.
Vs. R.O.B.
Bad stages - Battlefield, Dream Land
Good stages - Final Destination
*I'm on the fence with Lylat Cruise, having not played ROB here. The platforms could benefit his combos, but also throw off his approach and projectiles. Same for the constantly leaning stage platform. When I played Raffi-X, he picked Halberd since the small blast zone and platform are ideal for early kills with UThrow. However, it backfired. Also, him trying to recover from hugging the stage is suicide since you can hit him with DTilt, Dair, or Eruption. Point is, the fewer platforms, the better. Otherwise, he can setup Uair juggles on you or even DThrow, airdodge read, and USmash you at 80% for a kill.
Insufficient data for Meta Knight, as I have very rarely fought them, and none offline.
That said, I have no idea how Castle Siege, Halberd, and Lylat Cruise will work for us against most characters in the game. Unless you fight a heavyweight or another character whose movement is impeded, Lylat Cruise is not the most practical stage. Castle Siege leaves you with stage hazards, such as early kills on the walk-off of Part 2 and players forcing you to miss the platform of Part 3 or even the extra worry about gimping on there. It's a double-edged sword all-around.
Halberd, much like Lylat Cruise, features a slope that ruins our short-hop auto-cancels. We'll end up with more landing lag from aerials that will throw us off and give most of our opponents a free punish.
This post will be updated with more info. Please let me know if you have anything to add to the list.