I don't have a PS3, so I can't really say anything about Uncharted (although I have played it before).
Gears and Mass Effect are my favorite franchises of this generation though. I'm looking forward to Gears 3 more though because I've been a huge Gears fan since it came out in November of 2006.
I've heard very good things about the writing and overall quality of the campaign in Gears 3. Just read this article: http://www.gearscon.com/2011/08/camp...t-one-preview/
Sure, I'm extremely exited about Mass Effect 3, but it doesn't seem to be adding as much stuff as Gears 3 is. Epic Games has made a shitload of improvements, while Mass Effect 3 just kind of looks the same. The story in ME3 is probably going to be un-****ing-believable though. Bioware knows their shit when it comes to making a good story with rich characters and atmosphere.