There will never be a "best" skin as we all put different demands and wishes into our skin-wishlist.
Coming straight from MediaPortal I'm kinda in between atm. I was really hoping there would be skins like Maya
so I've ended up on reFocus atm. I kinda hate the OSD in the video player there though, so, yeah.
I have to trow something in tho. I have NOT contributed anything to XBMC myself (yet?) so I know I should be really happy just getting it for free. And the skins do look great! They're just not dialed in 100% after my prefs, but hell, just like I'm the definition of perfection in this world
I'm hoping it's possible to mix 'n match as it is in MediaPortal (copy OSD files from skin A to skin B, etc.
Oh and XBMC totally outperforms MP when it comes to built in flexibility, and the fact that you don't need a seperate settings-app is great.