depends on the size of your system imo. A small system 60g or under I would do 2part until the demand got really high. Anything bigger I would start thinking reactor. Reactors are less expensive in the long run but in a small system if they are out of whack things go bad fast. Dosers are harder to nuke your tank :) = more full proof, but a properly tuned reactor is great too. Reactors inherently create more stability which we know our sps love. Properly set up dosers will work just fine too. Oh reactors take up more space = con on small system.