What's he definitive version of Sonic CD?

I'm just gonna say the SCDR is overrated, and I have came with 3 reasons why so (just an opinion)

1- Really lacks on content compared to SCD&K, only adding some unnecesary extra routes and playable ESA amy. SCD&K had the ability to activate TMS, add smooth rotation, freely customise the soundtrack and more content that made it fresh n' unique.

2- Amy pretty much lacks of personality, it's just given and double jump and the SCD sindash, EVEN ORIGINS HAS SOME PERSONALITY GIVING IT THE PIKO HAMMER.

3- The mixed music it's decent, but it the default option already it's just a pain in the ass, it would be cool as content got after completing th game, but instead, you're trapped with it since second 1.

Origami

Although I prefer playing as Sonic, I will say that CDR's Amy is the better one. The double jump gives you actual different ways to approach levels instead of just being able to to the haha hammer spin. Era accurate too, so she doesn't feel a little out of place.(That's how Origins feels to me, at least.) I mean, it's so good that it predicted how they designed her in Superstars

I think it comes down to gameplay (and I'm confident that's why CD-R got the most votes here)

CD-R fixes the levels so they play like they were originally designed to play. Tons of previously broken launches/bounces/jumps were restored along with collision and physics corrections that just go a long way to making the game flow.
You can jump over CC3 with the Super Peel Out, you can bounce off the badniks to get on top of TT1 at the beginning, you can roll into the spring at the start of QQ1 to get launched a quarter of the way into the stage...and the Special Stages actually control properly like in CD93 along with the UFO's having their old hitbox. So no more clipping through UFO's for no good reason.

CD-R comes with CrowdControl, Randomizer, and a new game mode on top of having a Leaderboards button that actually takes you to the real leaderboard...Amy isn't supposed to be anything more than sprinkles on the icing of the cake. The cake is the gameplay; the fidelity restoration to the Music, FMVs, and SFX is the icing on the cake.

The other joint is just the regular CD11 with a 7 page long Options menu with options like Disabling the Super Peel Out, changing the HUD to other game styles, titlecard color options etc. that don't actually fix anything with the gameplay on top of being glitch ridden for the last two years. Its mission statement is just to conglomerate as many other mods as possible and has been caught stealing from at least one other mod in order to do so.
Right now most CD mods are going to wind up including Knuckles+Origins Amy because using the Origins Data File means you get to use them in the latest Decomp Update as long as you built it yourself to do the DLC checks, so even the aspect of "its got Knuckles!" isn't unique to it (nor was it ever). Nor is having a Super form as two other mods do that too (and will now have Knuckles/Amy in them as well).

Sonic 3 AIR is typically considered definitive because of its gameplay accuracy *and* being feature rich. Well Origins is a feature rich Sonic 3...is that better than the original? I'd certainly rather plug my Genesis in and drop in my Sonic 3 cart all over again than boot up Origins ever again.

Speaking as someone who has been a part of CD's community for the last 15 years, our active player base that streams/hops on calls with each other/strives to take the game to its highest level is about 4x larger than it has *ever* been (zero exaggeration). It exploded last year thanks to Sonic CD Restored and got even bigger over the summer with some Origins Knuckles hype thrown in there.
Anyone is free to come chill with us as we're teaching people how to play CD like it's Sonic Unleashed in there almost every day of the week. Players are generally shocked at how easy it is to go that fast and certainly everyone is capable of playing Sonic CD like that. : )

As far as lag goes, it runs off a fork of the latest Decomp so should only lag as much as that does. No changes to the way it renders anything were made. Also included is a Legacy.exe for older PC's based on the old 1.1.2 Decomp which ran much faster on slow PCs.
And no you're perfectly fine. I totally get why people would value the Elemental Shields; quirky little thing about Shields+ being a stack on, they don't have permission to use Shields+ in their mod and that's why it's built around mod stacking to get around that.

Restored's .ini file has Linear Filtering enabled by default (same as the original release of CD 2011) which, while completely not popular in any way, is due to it looking closer to how the Sega CD looks hooked up to a TV and staying faithful to the original Steam release.
Change ScalingMode to 0 and you'll have Nearest Neighbor unfiltered crispness.

I don't think you're bias, and your view is completely legit! CD-R is based on the idea of experiencing the original game at its best, so elemental shields and super forms weren't really on the docket because then it's not really the original game anymore. I'm honestly shocked Restored went over as well as it did with people, because I never really expected it to be popular due to the nuance of it.