both bulbs listed will "work" id go with a bunch of 26W CFLs placed strategically....how many plants are you growing? what stage are they @? if you can look for the CFLS that are U shaped & keep in mind most of the light comes from the sides not the tip!
42's are really nice too, you'll notice the difference. When germinating the same seeds in a hydro setup the plants that had the 42watt lights had roots hit the deep water (6"down) 3-5 days earlier.