If you are looking a scope for your rifle, here are some tips for taking in mind:
First of all, you should understand the scope’s anatomy and how it works and then you will be able to choose the best scope for you.

Pigeon hunting in Argentina

What power scope do I need?
That depends on what you are using your gun for. For hunting, if you limit your shots to 100 yards or less for big game you don’t need any more than 7x. For 100-200 yard shots 7x to 9x is good. Over 200 yards 9x to 12x is required. Here’s some guidelines:

Squirrels: up to 4x
Varmints: 4-12x
Big game in dense woods: 1.5-4x or 2-7x
Big game in fairly open country: 3-9x or 2.5-10x
Big game in wide open country: 4-12x or 6-18x

8 Rules for Chossing Rifle Scope for dove hunting

1] Don’t buy a scope that makes you sound like you’re lithping. Since Stith was bought by Redfield, this is no longer a problem.

2] You don’t have to spend top dollar to get a first-class scope. The very best (and therefore most expensive) scopes are better than instruments that sell in the $200–$300 range, but do you need one? Of course not. In the past year I have used scopes in this price bracket by Nikon, Cabela’s, and Simmons, and I don’t see what more you’d need to kill some poor dopey animal.

3] The most overrated quality in a scope is brightness. Bright is good, no doubt about it, but there is not a scope on the market that will not let you shoot from legal first light to legal last light. If you would like to buy a superbright scope and stretch the legal times somewhat, be sure to rehearse your explanation to the game warden beforehand.

4] The most important quality in a scope is toughness. A scope must hold its zero even when bashed, smashed, and trashed; it must adjust accurately; and it must not leak. You want my nomination for a tough scope? The Bushnell Elite 4200. I have owned something like a dozen in the last 15 years and have never had one screw up despite tons of use.

5] The second most important quality is resolving power. “Sharpness” is another way to put it. You want to be able to pick the brown-gray deer hide out of the brown-gray background.

6] Eschew complications of any kind. Eventually, they will bite you in the butt. You already know this: The more complex the machine, the more likely it is to break, and at the most critical time. Murphy (he of the Law) never sleeps. Also, complications always add to the cost of whatever you are buying, including scopes.

7] You don’t need lots and lots of power for deer hunting. Anything over 10X is wasted and adds to the scope’s weight, size, and price. It’s worth remembering that for years Marine Corps snipers were expected to hit man-size targets at 1,000 yards with fixed-power 10X Unertl scopes, and if the jarheads could do that, why do you need 16X to shoot a deer at 100 yards? If you hunt in the brush, you want something in the 1X–4X range or so. For all-around use it’s hard to beat the popular 3X–9X.

8] Shine belongs on shoes, not on scopes. I used to use shiny scopes, but that was before matte-finished models were available. If anything says “Run for your life!” to a deer, it’s a flash of reflected sunlight from a scope or a rifle.

(Source: Eight Rules for Choosing a Scope When Hunting Whitetail Deer with a Rifle or hotgun http://www.fieldandstream.com/node/1005010805)