OP would you mind posting some links, or at least specifying the year/types for each bike? I'm finding it hard to believe a Cervelo R3 with Ultegra is the same price as a Giant with a 105, if they're same model year, everything else being equal. You see the bikes I own ('18 S3 SRAM eTap, 19 TCR Adv SL1 Ult Di2, '18 SuperSix Evo Ult Di2) and at list the Giant is generally a little cheaper than Cervelo and Cannondale, all things being equal. Different model years may explain the price differentials. Are they all rim and/or disc brakes? Are they all using current Ult/105 groupsets (R7000/8000)?
As others have said, you should really ride and decide. They are pretty different bikes offering different rides. Two are light racing frames (SuperSix and TCR) and one is an aero frame (S3).
Between my racing frames, I greatly prefer my TCR, but I have the top-line model while the SuperSix was the mid-line model, so not a totally fair comparison. I found the TCR lighter, just as stiff, and way more comfortable than the SuperSix. My SuperSix is currently on a wall hanger.
Between the TCR and the S3...on flats and descents, going all out, I can squeeze a little more speed out of the S3...but at a noticeable cost of comfort. If I'm riding on well-maintained roads, for long, unbroken stretches, trying to set PRs or beat other riders, then I'll opt for the S3. For most other riding (which is the majority of the time) I'll opt for the TCR.