Well, I have an experience with several scopes in this price range including the Nikon Prostaff. The others I've used in this price range are a Bushnell Elite 3200, a Burris FFII, and a Leupold VX-I.
That also being said, you can also now pick up a Prostaff for $100 on sale right now.
Okay, in it's original price range of $150-160, I don't think the Prostaff is a very good buy. It's a decent scope don't get me wrong, and it does great at holding zero, but it's just not up to par with some other scopes you can get for around that price range. The turrets are a really pita as they require a coil or screwdriver to adjust so you can forget adjusting it in the field. That's something that wouldn't bother a lot of hunters though, but I just felt the turrets left a lot to be desired. The seemed to track fairly close to what they claimed, but I didn't think each click was exactly 1/4". It was really hard to tell, but it seemed like it was 3 clicks to an inch at 100 yards. No big deal. I didn't check to see if the scope was repeatable or not, nor did I do a box test so I can't comment on it there.
Now onto the glass. The glass is very similar to a Simmons Blazer that was on this rifle before the Prostaff. I had a really hard time telling a difference in the glass, but the Prostaff seemed slightly better in bright sunlight. The Simmons just seemed to have a slight bit more glare in direct sunlight, but it wasn't much of a difference and you'd have to be comparing them side by side to see any difference at all and then it was hard. In low light these two scopes looked identical. They both were decent, but nothing great. The Simmons was a lot better than you'd expect for a $40 scope. That being said, the tracking on the Simmons was way off. It seemed like at one part of the adjustment range each click was moving it close to 3/4" of an inch. I never checked it for repeatability, but I'm pretty sure it wouldn't be. The turrets felt way better on the Simmons, but they just didn't adjust it accurately. This was where the Nikon showed the biggest difference over the Simmons. That being said, once sighted in the Simmons nor the Nikon ever gave me any problems. I just put more faith in the Nikon, so I stuck it on there to replace the Simmons.
Now, comparing it to the others I've used in that price range the Burris FFII is the clear winner and by a decent bit. In the daylight it's more vivid and brighter than the Nikon, but the Nikon isn't bad by any means. The Burris is just better. In low light that's where the Burris really blows away the Nikon. It's quite a bit better imo in low light. I could see stuff clearly that I couldn't make out with the Prostaff when doing tests in low light. I could go into detail about my tests I performed if you are interested, but I figured I'd leave them out for now as this will already be long enough. As for tracking on the Burris, it seems to track relatively close. It's hard to tell for sure as the rifle it's on shoots 1.5" groups at best at 100 yards, but it's pretty close. The turrets are easily finger adjustable and these just blow the Nikon turrets out of the water. As far as durability, I've not seen any issues with the Burris, or any of them. You can also find the Burris scopes cheap on eBay and get one on there new for the price of a new Nikon Prostaff, when the Prostaff's are at their normal price. That's why I wouldn't recommend the Prostaff at their regular price.
Next up is the Leupold VX-I. This is by far the worst out of the ones I've tested. The turrets are horrible. They are friction adjustments so you can't feel clicks and they don't track anywhere near being close. These are the worst turrets I've ever used, and I'm really not sure why anyone would put these on a scope. Next up is the glass quality. It's no where near as good as the Burris. In the daylight it looks very similar to the Prostaff and the Simmons Blazer, but in low light it's even worse than both the Simmons and the Prostaff. Some of the stuff I could see the outline with with the Prostaff I couldn't even make out with the Leupold. Then it comes to durability, I had this thing for about 8 months. It sat for most of those, and then I noticed one day while hunting that when I shot it looked like the insides were shaking. I sent it into Leupold and got it fixed. I got it back and mounted it back on the rifle and sighted it in. It worked great. I then put it up again and rarely shot it. When I got it out about 8-9 months later to check it before hunting with it, I noticed that it would shoot 2-3 shots into a group then it would move several inches off and shoot a group. Then move again. Every couple shots it was adjusting itself. So I sent it off to Leupold again and got it fixed again. This time, I got it back and it's worked great since, but the adjustments still are horrible, and the glass is still worse than a $40 Simmons and on par with a $30 Tasco I've used.
The next VX-I I had, I got from a buddy. He got fed up with it as he had it sighted in. I saw him shoot it on a Friday. The next monday he got it out to show us how well it shot, and it was completely off target. Further inspection revealed it was adjusting itself every shot, about like mine was doing on his moved every time he shot. He sold it to me as he was fed up with it. I bought it really cheap and got it fixed. I didn't have anything to mount it on so I sold it. I did check out the glass, and it was identical to the other one I've got. It was pretty bad for a scope in that price range.
The other Leupold I've had was a Vari-X IIc. It's glass wasn't any better than the others, but I never mounted it either so I can't comment how it held up. The guy I sold it to says it works great.
A 3rd friend bought a VX-I and his wouldn't hold zero right out of the box. He got it fixed from Leupold and traded in for a .22. So myself, nor my friends have had good luck with the VX-I's, but apparently some guys have had good luck with them. Still doesn't offset the fact that you can get much better glass for a cheaper price though. One thing I will say about Leupold is they have a great warranty department and do take care of any issues you may have. If I was going to buy a Leupold I wouldn't get any less than a VX-II, and even then while they are decent scopes you can still get better glass for similar money.
Next up was the Bushnell Elite. The one I had was a fixed 10 power so it's hard to compare it to the rest which were 3-9x40's. I did all my comparing to this with the others on 9x. This was the tactical model and the turrets had a very solid feel to them. I loved these, but I'm not sure I'd want exposed turrets like this on a hunting scope. They tracked pretty darn close. I was shooting it at 50 yards mostly on a .22 that was shooting one hold groups. It seemed like it might be a tad off, but not much. It was very repeatable and I adjusted it several times and reset it to zero and it always reset. Glass wise, this scope was decent, but not great. In low light it was hard to tell since it was a fixed 10 power, but it seemed to be slightly worse than the Burris on 9x, but slightly better than the Prostaff on 9x and better than the Leupold on 9x. It was a good scope, but I ended up selling it just because it was too much scope for a .22 imo.
So the Prostaff is a great scope for $100 and I'm not sure that you can find much else in that price range that's as good, but for it's original price of $150-160 you can get a lot better glass for around those prices. Another great two options right now are the Vortex Vipers on clearance and the Nikon Monarch UCC 3-9x40's on clearance for $199. Those are two great deals on some great scopes.
Also for more reading here is a great writeup comparing several scopes in the $200 and under price range. This was written before the sales on the Vipers and Monarch UCC's so that's why you don't see those mentioned. They are a step above all of these though.
http://opticstalk.com/inexpensive-scope-comparison_topic21176_page1.html
