Depends on a lot of variables. Like size of the grow you hope to have. Cabinet, closet or room? Size of plants you want, SoG, ScroG, ventilation etc.
If it's a small grow the 175W could veg them nicely and a flowering bulb like the Hortilux EYE or one of the SunMasters in the 400W you're all set for buds.
The 400 will flower at max about 8sq', 50W/sq' tho 70W/sq' is better. You could run the 175 with the 400 if you don't need it for a separate vegging area.
Lots of ways to do it. Need more info to come up with the best way.