As far as Omegas go, I feel the two best are Luigi's Mansion and Norfair. With the former, we get all the best omegas have to offer. The strange lip of Luigi's allows us to still get stage spikes while giving us a wall to cling to (extra double jump). Additionally, I find it nearly impossible to die from bouncing off the side of the stage because the ledge itself, to my knowledge, cannot be bounced off of (we get pushed under it if we HP into it during a non-auto ledge sweetspot portion of HP and then grab it as HP ends). Even if we bounce off the side, we bounce right onto the ledge, grabbing it. Finally, Shadow Sneak is well-concealed. Norfair has essentially everything that Luigi's Mansion has except we can still potentially bounce off its ledge. On the other hand, Shadow Sneak is 100% invisible on that stage for some reason.
Edit: We should also be cautious of CPing omegas with grass as grass gives characters better ground traction for some reason, meaning our hyphen Usmashes won't slide as far (Duck Hunt is exempt from this rule thankfully).
As far as stages I personally really enjoy go, they're Town and City (low ceiling, platforms we can leap to with one jump, lots of space), Delfino (we can move around so much here, and the smaller blast zones can help us net early kills with Uair, Fsmash, Fair, etc.,), Duck Hunt (soooo much space, and we can leap to the top of the tree very comfortably with two jumps. The ducks also allow us to stall with Dair and the 2D nature of the stage allows us to hit with Fsmash up close), and potentially Halberd once I learn the timing to punish airdodges onto platforms with Usmash's second hit (Uthrow essentially kills 20% earlier on Halberd, not even taking into account grabbing someone on that platform).
As for stages I don't like, those would be Battlefield (high ceiling, irritating platform arrangement, and little space to run around, but still good in certain MUs, especially as we can still apply pressure on platforms via Utilt and Bair), Smashville (people can sit on that platform, surprisingly safe from Greninja, and it's small), Lylat (imo, the worst stage once Kongo is out. Limits our Shuriken game, platform arrangement is horrendous for Usmash, even making timing that second hit on airdodges differ depending on the stage's tilt, another high ceiling, and Shadow Sneak can potentially glitch Greninja into the middle of the stage only to fall through it), Castle Siege (first phase is way too small while third phase's tilts are very awkward for Greninja, but the second phase is at least wonderful for running away), and of course Kongo Jungle (Barrel can thwart attempts to recover low, ceiling is ludicrously high, and the divot hampers shuriken use, but at least we can circle camp fairly well here).