Joel Kramer

Paramount US 4K Blu-ray > Capelight DE 4K Blu-ray (caps)

Although the provenance of Paramount's 5.1 track is not confirmed, the fidelity is outstanding and speaks for itself.
The 7.1 track on the Capelight/old Lionsgate release is just an upmix with nothing gained over the 5.1.
The original stereo mix is only present on older DVDs and LaserDiscs; all Blu-ray 2.0 tracks are downmixes.

Paramount 4K Blu-ray has no extras, Capelight 4K Blu-ray has most of the extras, Olive Films Blu-ray has a exclusive commentary

• 2015 Lionsgate Blu-ray (but it's missing the extra scenes in the Ultimate Edition)

• 2017 StudioCanal 4K Blu-ray and subsequent 4K Blu-rays are notorius for being heavily denoised and smoothened. Alternatively, 35mm scans for the theatrical cut is also available.

• For the Ultimate Edition with the T-1000 searching John's room and the happy future ending, the 2009 Skynet Blu-ray, which is the older pre-2017 transfer, but has DNR.

Differences of mixes on various releases: see thread and more info here.

2017 Blu-ray (which has the DNRed transfer), the 2009 Skynet Edition Blu-ray, and the 2000 Ultimate Edition DVD have exclusive extras. The 2003 Extreme Edition DVD has some exclusive easter eggs.