the simple answer for flowtoys - buy two of every color and have fun, ahah
however, to try and answer the question - the white/blue flowlights are the brightest of the bunch, but the rest arent too far behind, and in a flowchaku situation, with 2 lights per stick, i find that usually the coolest combinations are one bright one and one not-so-bright for contrast... made a short video demo-ing some of the flowlight colors, should be processing now..
I dont have Earth or Love, and i have a few that they dont currently offer.
http://www.flowtoys.com/pages.php?pageid=25#flowlightcolors is the list of currently available colors at any given time.