Who would you start?
Let's say Tynes is 100% ready.
I'm going with Carney. The guy is having decent kick-offs and perfect so far in fg's.
Keep them both on the roster. No sense in trying to fix what isn't broken imo.

Oh and btw, Carney was named nfc special teams player of the week.
http://www.nydailynews.com/blogs/giants/2008/09/carney-named-nfc-special-teams.html

I must admit I am alot more comfortable with Carney than Tynes

but at the same time Tynes has certainly earned his chances with this team, particularly in Green Bay last January