If you don't carry more than one wedge or if you already have a battery of favorite wedges that you've used for a while, the question is "when should you update your wedge system?" The part of your club that wears out first is the face, and there can be damage even if you can't see it. According to a study done by Golf Magazine, worn grooves are a huge detriment to your game. Their research proved that a wedge with fresh grooves produces twice the backspin and distance control.
So if you don't have the right wedges or if you've been playing with the same wedges for more then two years, it's time to pony-up for some new tools. To help you make the choices I've selected the Best of the Best but I'll advise you as I do all my students: no matter how much information you gather - always try before you buy.
There are several things you should consider when choosing your wedges:  how do you add the correct wedges to your bag and still stay within the 14 club-limit imposed by the rules?  what is the best combination of loft and bounce? and  which manufacturing process do you choose, cast, or forged?
 I'd suggest you drop the long irons and make room for four wedges, a pitching wedge [PW] with a loft of say 48 degrees, a gap wedge of 52, a sand wedge of 56 and a lob wedge of 60 degrees. Given about a ten yard difference for every four degrees of loft, that gives you coverage over four distances. Lets say for a full swing you hit your PW 100 yards then your 52 degree goes 90, the 56 about 80 yards and the lob 70.
 Bounce [the shape of the bottom of your wedge] determines whether a wedge digs into the ground or skids along it without snagging. Club-makers offer different bounce/loft combinations so you can choose a wedge that will accommodate your swing type [more bounce if you're swing is steep, less if its shallow] as well as the course conditions. If the sand is soft and fluffy you need more bounce to keep the clubhead from getting stuck; in wet sand or on hard ground, you need less bounce to keep the clubhead moving freely.
 The third key to choosing the wedge that's right for you is feel. There are forged wedges which are soft-feeling at impact but the grooves wear more rapidly. And cast wedges, more durable but not as feel orientated.