Both are viewable in non extreme lighting conditions. I have both 2011 15inch glossy and anti glare before i returned the glossy.
IMO, glossy is slightly better colours (vibrant) than glare (NOT BY MUCH!!!).
The glare is useful only if moderate lighting conditions kicks in. In extreme lightings, both glossy and glare looks ugly (non readable from normal viewing distance).
I have been living with 2010 15inch glossy for a year and i made a switch because i fell in love with the silver bezel on the anti glare. its does looks more classy and suit in the whole unibody design (silver around the black keyboards, silver around the black lcd? anyone agree?)
While the black bezel glass covering the glossy sure looks cool too (unique like iphone, ipad black - dont have words to describe it sorry)
Like everyone said, i agree with them, YOU CANT go wrong with eithe rof them. They are of still good image quality screen compare to a lot of other PC laptops and older model Macbooks.
Cant adapt glare on glossy screen, wash out on glare, choose this over that, and bla bla bla...these are all not a good reason to choose the screen after i have experienced both. Its all up to personal preference on how your MAC you wanna look like when using.
Does not matter how many pros and cons about the screen, choose what your heart tells you (like said, you wont go wrong with either ones)