In my opinion SunMaster bulbs and Eye Hortilux are the best bulbs on the market for horticultural purposes. Selecting the correct bulb can make all the difference in your grow op. Her are the website links for these two manufacturers for your reference.
www.eyehortilux.com
www.sunmastergrowlamps.com

Make sure to download the .pdf files of the bulb you intend to purchase. It will give you detailed information on the bulbs mortality rate and actual wattage used. As for your question Metal Halide is need for good vegitative growth as opposed to High Pressure Sodium lighting as it will be needed for the flowering stage. If you can only afford one go with the HPS bulb such as a Eye Hortilux Super HPS as it provides 30% blue spectrum light which will mimic some properties of a MH bulb. If your ballast is not a switchable model [MH and HPS] they also manufacture Conversion Bulbs for use with non-switchable ballasts. This website has the best prices on bulbs I have ever seen on the internet and you will save big cash.
www.hydrowarehouse.com
I hope I was of help to you. Have a good day freind.