I have used sunmasters, hortilux digilux, growbright and ultrasun (ultracheap). They all work well. The only failures I have had were a 600W Sunmaster MH conversion that didn't last more than 4 months and a Digilux 600 HPS that had a significant malfunction (capsule ruptured, molten sodium coating the inside of the outer sheath). So I think any bulb will do, just be sure to seat it firmly in the socket (major cause of early bulb failure being lack of so seating).
I've got a nice fresh ballast story for ya though. When I was working in my veg room a couple weeks ago I noticed one of my 600s was flickering just a little bit. Then it started flickering more. So I turned it off, let it cool down and switched in a brand new bulb. Turned on, warmed up. after ten minutes crazy ass flickering and a certain sound and the strong smell of ozone. I went straight to the breaker box and cut everything.
Shot an email to HTG supply, said I had 6 of their ballasts and some were under warranty and some are definitely out but damned if I know which are which and can they shoot me a deal on a replacement. They got back to me and told me to call Tony (love that guy). explained the problem, he looks at all the shit I've bought from him and says you are a valuable customer; what can we do? I said I wanted another ballast, but 1K this time and another big kahuna reflector and a few Sunmaster HPS bulbs as well. Just shoot me an invoice to my email and I'll paypal it.
Okay, this rig as specified at HTG is about $560 delivered to my door. The invoice I received totals $345 including shipping. I don't buy anything but lights there, but I wouldn't go anywhere else with that kind of service.
So now I'll be running two matching 1Ks in flower. I'm still vegging under 600 though guys
whats the best 600w bulb?