Viscoat (Chondroitin sulphate) is dispersive in nature and because of its prolonged retention in the anterior chamber, it is more effective endothelial protection. It is also a cell membrane stabilizer. A stressed cell that might be near death can be preserved if it is coated with chondroitin sulfate. Chondroitin sulfate is also a free radical scavenger. It has been reported that phacoemulsification generates a significant amount of free radicals and by using viscoat, we can prevent this damage.

You can refrer:

Vasavada A, Ong M, Cordova D, Hartzer M, Protective Effect of Ophthalmic viscosurgical devices (OVDs) against hydrogen peroxide-induced oxidative damage to corneal endothelial cells: an in-vitro model. American Society of Cataract and Refractive Surgeons; April 3-8, 2009; San Francisco, CA.

Aguilera F. Prospective Nonrandomized Comparison of Viscodispersive OVD (DisCoVisc) and Dispersive, Cohesive, and Supercohesive OVDs in Uneventful Cataract Surgery. ASCRS Meeting; April 7, 2008.

I am totally in agreement that Viscot in my experience provides a better protecion of the   corneal endothelium in hard cataracts. 

Viscoat is also slightly hyperosmolar which helps draw fluid out of the cornea, facilitating the endothelial function and keeping the cornea clear.   So it not just protection, Viscoat also has a direct beneficial effect on corneal clarity, even should the endothelial cells be slightly compromised.

The hyperosmolarity can be taken advantage of during e.g. intraocular surgery if the view is already compromised due to mild to moderate corneal edema, the cornea will clear after filling the AC with Viscoat, in about 20 minutes.

McCannel CA.  Improved intraoperative fundus visualization in corneal edema: the Viscoat trick.  Retina. 2012 Jan;32(1):189-90. doi: 10.1097/IAE.0B013E318232AE26.

I agree entirely with all my respected colleagues.

I agree with all of the colleagues, but there is no viscoelastic in the World that can protect corneal endothelium if the surgical technique is bad. So, focus more on the phaco parameters, technique itself together with the proper viscoelastic.