I decided to replace the standard pedals on my Giant XTC 4.5 with something a bit grippier after finding that I was slipping off when trying to adjust my feet position, 
especially when the trails are muddy. After looking around for advice (especially on bikeradar.com’s forums) the general consensus is that DMR V8/12’s or Wellgo MG1’s were the best bet. I decided to go with the MG1’s as they were cheap (£35 delivered from Merlin Cycles), relatively light (made from magnesium) and not as prone to the paint chipping as the DMR’s.
Compared to the standard pedals they are definetely lighter and a million times grippier. The screws that protrude from the pedals to give grip go amazingly well with the Etnies shoes that I ride in. Once your feet are stuck down on the pedals in one position there is almost no movement at all, if you want to adjust your position you have to lift your foot from the pedal completely, which is a bit of a pain if you are standing up priming for a jump and need to adjust position.
If your looking for a new pair of pedals then I would definetely go with Wellgo MG1’s. I definetely think they improved my riding, especially in the mud. They make you feel a bit more connected to the bike and in control.
Also the service from Merlin was awesome. I ordered them about 8pm Monday night and they shipped first thing Tuesday morning, arrived 10am Wednesday just in time for my to take them to Drumlanrig for a test run. Considering the Hong Kong sellers on eBay are selling them for around the same price I definetely can’t complain.