Best Vinyl Bach - Solo Cello Suites recording?

The Starker set on Mercury is exceptionally well recorded. The Speakers Corner reissue, still available new, is very well done. The sound is immediate, with high impact. It is relatively closely miked, so there is not a lot of hall ambiance in the sound field. What you get is the sound of Starker and his cello sitting immediately in front of you.

For another beautifully well-recorded set of the solo sonatas, there is the Helmerson recordings on BIS (LP5, LP25, LP65). You'll have to hunt the used market for these three records as they've not been reissued. The Helmerson performances are more distantly miked and capture the wonderful reverberation of the church in which they are performed.
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I cannot tell you how the Mercury Living Preference reissue of the Starker compares with the Speakers Corner, but I can tell you that it is very, very good. Should be relatively inexpensive as a used set.

If you want a heartfelt power performance, Rostropovich on EMI is unbeatable .
If. like me, you want an elegant performance, Fournier's is the most profound . DG 449711-2. remastered to better sound than is normal for DG.

I never heard a bad recording of these masterpieces .