I really cant say, i havent used MH or HPS for veg yet. ive seen many HPS vegged plants and they are too lanky, not many nodes for the height they get, etc. and mh is probobly good, my plants vegged as fast under cfl's and 1 cool white (blue spec) floro tube when i first started out. very tight nodes. I started 12/12 on them on the cfl's a week before i got my hps and switched.
Here's a pic from 1 minute ago, doing quite well.
Knowm grew a grapefruit i believe, i forgot the total yield, it was a very good yield, and i believe there was 1 17 gram bud. using 8 42 watt cfl's.. im not saying they are the best, i'm sayign they are a very useful alternative for someone who cant afford to go buy a HPS or vent it's heat.