Approaching nine years of non-stop EMS work, so a fair proportion of real rough ground work - give me skids every time please!! Quite right that three wheels might be more stable once settled - however as you are lowering yourself gently among the surrounding boulders the wheels have a charming habit of finding the lowest spots to settle into while the aircraft skin is likely to find the highest pointy rock. Skids let you feel the 'average high spots'and if it does not feel OK you just have another go!
Also wheels sink, i've found no better combination than skids and anti-sink plates.