Also, to input myself into the glofish discussion, from what i've always understood they are not infertile, the first generation is inserted with the gene that makes them glow and then after that it is passed down and inherited.
This is also what it says on the official Glofish site, http://www.glofish.com/faq.asp
"Do you have to add a fluorescence gene to every fish before it hatches?
No. Today's GloFish® fluorescent fish are bred from the offspring of fluorescent zebrafish that were originally developed several years ago. Each new GloFish® fluorescent fish inherits its unique color directly from its parents, maintains the color throughout its life, and passes the color along to its offspring."
"Does the fluorescence harm the fish?
No. The fish are as healthy as other zebrafish in every way. Scientists originally developed them several years ago by adding a natural fluorescence gene to the fish eggs before they hatched. Today's GloFish® fluorescent fish are bred from the offspring of these original fish."
So according to them, glofish are just like zebra danios except they glow. The second claim I'm skeptical on as it may be somewhat marketing bull, but as for the first I see no reason why they'd say something that isnt true about breeding them.
Personally I have three glofish atm, (had for but the yellow one died and just havent gotten another one). In my experience they do do better in higher numbers, even four is better than three. As for colors my pink/red and the orange one are the brightest with the blue being the dullest. Yellow/green is in the middle, and I've never owned purple.