Hamilton's are the cheapest that I can find and come in a 10k and 14k. I currently use an AB 10k and an XM 10k and I plan to go with all XM bulbs. Since they are white as white can be, I plan to supplement them with dual 6 foot actinic URI bulbs -
I just switched over to 250watt radiums on a pfo hqi ballast. My previous bulbs were aquaconnect 14k. The AC's are a bit pricey but nice. I am actually surprised at the intensity of the radiums. They almost have the same intensity of the AC's. The reason i went with these is i want to see what effect 20k has on my corals.
I think the ushio is a nice bulb. If it's working for you, why change it. XM's are good too. There's so many good choices that it's hard to make the wrong choice. It all boils down to what you like, the bluish look, or the whiter look.