I've used the Sylvania Cool Blues and Silverstars and have been pleased with both of them. In my opinion the Silverstars are a little more pricey than they should be. $50 for the pair seems to be kind of high. I bought 9006 bulbs and then modified them for my 9005 sockets. That was the only way they were worth the price. The Cool Blues are worth it at around 10 bucks per bulb though. They aren't even blue. Very white light. Much better than stock.
