There's also the case where the Mac Port will not work, but I'd need further confirmation from a Mac user.
The App Store version of CS+ doesn't work by itself. Technically Apple broke it by changing the way relative paths work, but Nicalis hasn't fixed it yet, and I doubt they ever will. There's a fix
here, but the Mac version doesn't have the Machine Gun Challenge, updated seasonal themes, or replay support like the Steam version, so don't bother.
Since I'm posting though, I guess I'll list my rankings of the ports. I'm ranking them based on their quality alone, so I'm not going to bash X port for being "just Y port but with more features", since that would make X port objectively better.
1. Switch. Never played it, but it has the most challenges, soundtracks, and quality of life changes. 16:9 aspect ratio, OG and New graphics, strafing, and probably some other stuff I'm missing.
2. Steam. Second highest on challenges, has three soundtracks, OG and New graphics, updated seasonal themes, and replay support. Can be modded more easily than other ports due to being on PC, and access to Profile.dat means infinite save files.
3. eShop. Four challenges (five in the Korean version), 5:3 aspect ratio, nice 3D graphics, and Curly Story Easy and Hard modes. No New graphics or soundtrack, but I think the gameplay additions put it above WiiWare. Also, the 290 Counter keeps moving while in the pause menu, which is utter BS.
4. App Store. It's WiiWare but with Wind Fortress, no lag on New soundtrack, better sound and graphical quality, and extra options. Like Steam, can be modded due to being on a PC, but Steam makes a better base due to more features.
5. WiiWare. Two challenges, OG and New graphics and soundtracks. Long pauses with New soundtrack and poor sound quality set it back. Also, Time Attack plays the item fanfare every time you choose a weapon.
6. Freeware. It's not 40 bucks like CS3D, 50fps instead of 30, and is the easiest to mod (barring CSE2).
7. CS3D. The 3D graphics were something new, there are new areas (although I thought the extensions to already long areas were unnecessary), and it had a fun glitch to use. Only challenge is Time Attack, "Classic Mode" isn't even classic and shares saves with Story Mode, the controls were flipped for no reason (though you can just use X and Y instead), the game is capped at 30fps, and only one soundtrack is available.
8. DSiWare. Only challenge is Time Attack (given, it's the best version of it), and the screen is crunched to the DSi's resolution.
But we all know CSE2 is the best, since it's basically freeware but without limits, and has the potential to be the ultimate Cave Story build.