Strictly the bulb. Well, fixture design does play a part, but most of them are very similar until you get to the really high end stuff. Personally, I like the 6000K Daylighters in a 4ft. I wouldn't try to paint under them, but for general purpose, I like the higher K (also a bit of a mood lifter in the winter). I'm going to swap out all the lights in my windowless office to the 6000K for the winter so I don't get depressed. LOL!
I can't remember if Menard's has the comparison chart like Lowe's, but most stores that sell a lot of fluorescents have a chart that shows what temp is best for different applications. And don't worry if they're a few bucks more - fluorescents last forever so it's not a huge expense to spend a buck or two more a bulb.
*Thank you for mentioning Menards...now I have that dang jingle in my head..."Save Big Money at Menards".
