Have been playing with the Pure Storm GT for about a year. Recently demoed the Pro Staff Six.One 95 fairly extensively during my search for a new stick.
Let me start by saying these racquets are nothing like the other. The Pure Storm carries it's weight in the head, being 1 pt HL while the Pro Staff is 7 pts. HL. This is a major, major difference. The swingweight on the Pro Staff is much lower, forcing the user to generate much of the power whereas the Pure Storm will give you more power from the weight in the head.
The Pro Staff is more of a player's stick (although some "purists" would still consider it a stretch to call it one) while the Pure Storm is closer to being a standard Babolat that has a slightly smaller head size.
If you're dead set on getting either of these I would say first consider your rating. If you're not a solid 3.5 or higher, I don't think I be able to sleep at night if I were to recommend you play with the Pro Staff. The next is the power you're able to generate. If you want more without going to an all-out Babolat style (Aero or Pure Drive), go with the Pure Storm.
If you want a Babolat similar to the Pro Staff, look into the Pure Storm LTD GT. If you want a Wilson similar to the Pure Storm, look into the BLX Blade 98.
For the record, I switched from the Pure Storm to the Pure Storm LTD GT while looking for less power and more control. The LTD and Pro Staff were incredibly similar, but something about the LTD felt more comfortable to me. Can't explain it - maybe maneuverability, but I knew it when I played.
Good luck in your search, be patient and don't rule anything out before trying it.