Even with all the great replacer options on the Nexus, I still like and prefer the vanilla Skyrim horses. That said though, I thought their meshes could do with a bit of a facelift. I have upped the polygon count and smoothed the meshes of all vanilla horses, Shadowmere and Frost.
Those with a keen eye will also notice that I removed the additional "hair" meshes from the hooves, belly and cheeks of the horses. To me, these just look bad no matter what retexture you use and I think their absence actually improves the look of the horses.  

Additional suggestions:
I make use of the following additional mods to achieve what you see in the screenshots. All of these are highly recommended. Load order priority as per list:

• HD Reworked Horses 
• Yee Haaaa Horse Saddle Retexture
• Higher Poly Vanilla Saddles
• Higher Poly Vanilla Horses
• Your preferred unique replacer, if applicable.
  

Note on 5: If you prefer a different replacer for Shadowmere, simply have that mod overwrite my file. Frost does not have a unique mesh, so any replacer mods that replaces Frost will make use of an ESP/Plugin and will thus overwrite my version of Frost by default. 

Main Files 1 & 2:
It was recently  brought to my attention that the horse mesh was changed for the Anniversary Addition to accommodate horse armor. I have accordingly created a version of High Poly Vanilla Horses that is compatible with AE. Kindly ensure you make use of the correct main file.
SE / VR = Game Version 1.5.97
AE = Game Version 1.6.xxx.x  

Main Files 3 & 4 - Fluffworks Versions:
I have added two files that patches the Higher Poly mesh with Fluffworks. Two files are available to correspond to the two versions of Fluffworks: Medium and Quality. Choose whichever matches your Fluffworks version to ensure similar quality. All Fluffworks horse meshes are included in the patch. Overwrite Fluffworks. Choose only one main file.
Update - Main Files 5 & 6: I have added versions of the Fluffworks horses that are compatible with the Anniversary Addition (AE).  

Main Files 7 & 8 - Realistic Horse Breeds:
Higher poly horses for the brilliant Realistic Horse Breeds by KrittaKitty. Two version available, one for SE and VR and one made compatible for AE.
 
Compatibility:
This mod replaces only the mesh files, no plugin/ESP included. No textures are included in the download, your own load order will determine the actual textures used.

Installation:
Use your preferred mod manager to install as per normal.
Overwrite if prompted / give my mod priority.

Credits:
Realistic Horse Breeds by KrittaKitty
Fluffworks by Macxhiin
Blender by The Blender Foundation
NifSkope by Alphax, m4444x, tazpn, wz, Shon, amorilia