Red Sea's is the worst, IMO. Plantguild makes a powered diffuser that works pretty well for me, but it is big and instrusive. I use Hagen ladders on three tanks, a 10 gallon and two 20 longs. They take up the least space and they work pretty well. They require a sort of Zen attitude- they have to be dirty to work well, and snails will wander through and knock out a few hours' CO2 and you just have to let them be. I use one glass diffuser from Aquamagic that has been trouble-free for one year. Another one I got somewhere else clogs up constantly and I stopped using it. I use PH/KH readings to determine how much CO2 is being delivered, and the good glass diffuser seems to do the best of the whole bunch.