If you know what your doing you can have 100% sucess with jiffy pellets....
I go with a cheap plastic dome from the hydro/garden store and the dirt pucks that expand in water. Cut on 45 degree, scrape and score stem, dip in rooting gel and insert into puck. Squeeze of extra water from the top down ensuring that the dirt squeezes firmly arround the clones stem and dome it. I keep mine coverd with a white towel that allows ambient light for the first 3 days(i read that this allows the plant to focus on root developement and less on photosynthesis for the first few days) then remove it. On day 5, I move the dome top a couple of inches away from my fluorescents. As long as your room temp is right (mid 70's to mid 80's) and the moisture level of the puck is kept damp dry....NEVER dripping wet, then you should have fast results with good sucess. I cut 20 clones at a time, every 4-6 weeks, and in over a year have had only 1 single failure using this method.