Bulbs and Ballasts

Are there big differences between the different bulb manufacturers? I'm surfing eBay to buy one and for 600w bulbs they all make the same claims: 24,000 hour life, 30% more blue then standard hps and 95,000 lumens. Does it matter which I buy?

Same question about digital ballasts. Why are some $160 and others as much as $320 that seem to do the exact same thing.

Thanks, YGB

beter light spectrum and some longer life