SMCO http://www.nexusmods.com/skyrim/mods/13529/?

DDS OPT http://www.nexusmods.com/skyrim/mods/5755/?

Optimizer textureshttp://www.nexusmods.com/skyrim/mods/12801/?

Which is the best?

Out of those three - DDSOpt, without a shadow of a doubt

Its mipmaps are the most detailed of any of the optimisers ( no surprise there, Ethatron wrote his own custom code for creating them, whereas the other two I think just use Direct X routines ( DXT Format ), they do not know how to handle some of the special case textures properly even though for the purpose of optimising they do a good enough job from what I have heard )

It needs a little more study to get to grips with http://wiki.step-project.com/Guide:DDSopt

Oh and the STEP Team have already done all the vanilla textures using the above guide :

From the Optional files here ..

http://www.nexusmods.com/skyrim/mods/11/?

.. Grab the file "STEP Optimized Vanilla Textures - Standard Version"

But the best way to optimise textures, is to get to know all the different types of textures intimately, and the use of them in game, and use Photoshop ( or G.I.M.P ).

Also see this topic http://afkmods.iguanadons.net/index.php?/topic/4283-all-about-textures/

This subject is a lot more complicated than many people think.

Edit : Hint .. there are a lot more very nice topics at AFK Mods, in the Knowledge-base section http://afkmods.iguanadons.net/index.php?/forum/332-knowledge-base/

Thanks a lot for this link! There seems to be a lot of interesting Information there.

Thank you!