I'd like to use a thief for my next character and I want to know what are the best sneak mods out there ! I'm using also GCD . Gimme advice please ! :ninja:

My favourite still is JOG's http://mods.jo-ge.net/mw/index.htm.

Are you sure is it compatible with GCD ?

Yes. All bonuses/penalties are implemented as spells; no player attribute/skill is changed directly. I've been using both Enhanced Stealth and GCD for years now. They are compatible.
Also, here's an excerpt from Enhanced Stealth's readme file:

Thanks kind sir ! :foodndrink:

Any good stealth mods compatible with GCD but that don't require the troublesome MWE?

Before I found JOG's Enhanced Stealth, I was using the "Stealth Enhancements" (separate .esp file) from LDones' http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=1576. I'm still using the rest of this collection (Improved Lockpicking, Improved Open Spells, and Improved Trap Settings). None of these mods require any external program, and they're all compatible with GCD.

There is also this one http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=8636 but I don't know about GCD compatibility

There is also Tim The lighting mod I havn't used it yet or at least not for long , But it's sneak modifiers should be fine with GCD well I hope so anyway . I used Ldones for years with GCD without any issues at all.