HPS means High Pressure Sodium.
Link your tent selection bro, then we can help you out further.
Growing marijuana is all about flowering. If you favor vegging, you can get a very big and healthy plant with little popcorn buds. And if you favor flowering you can get a small healthy plant with massive buds potent buds. Plants utilize the blue of MH and the red of HPS during flowering and vegetation. Some people will tell you that you MUST have an HPS for flowering, and they may be right, but I would flower with a 600watt MH over a 42 watt 2700k cfl any day.
To break it down, if you can only choose one type of bulb, go HPS, You'll get better results than going all the way with MH. Many people go HPS full growth perfectly fine. Supplement with some 6500k CFLs if your worried about spectrum during veg.
Also, most modern ballast run MH and HPS. And you can also google conversion bulbs, that may interest you.