My boyfriend and I have moved away from home which means he isnt able to use his Dads guns. He's always admired his over and under and I think thats what Id like to get him for Christmas...but I havent the first clue on what to get. Any advice? Thanks!!

Here is what I would get him, considering the info you gave;

http://www.stoegerindustries.com/fir...ger_condor.php

for a few bucks more - the "supreme" (better wood).

http://www.stoegerindustries.com/fir...ger_condor.php

For the money the Stoeger o/u is a good gun. I have had one for about 6-7 years and its a well built gun. I believe that Stoeger is actually owned by Benelli. Bottom line if your on a budget its a good gun at a good price.

What gauge should I get? Im completely in the dark about guns - all I know is his Dad is a police officer so he is used to some nice guns, and I want to get him one that he will be excited about. He is 5'11, not sure if that affects the barrel length? What is the benefit of a fixed choke opposed to a screw in? Just convenience? Thank you so much for the help so far!

I am another that likes the Stoeger Condor. I have one in 20ga and as soon as I get home I am buying one in 12ga.
For your question, get a 12 gauge allot of versatility in the 12 gauge

The Stoeger Condor is a pretty good workhorse. Besides ducks and geese, mine even works very well on roosters.

The Stoeger is a good work gun, I agree. How much were you looking to spend? You may look at the Brownings if you wish to step up a bit and if he is more used to top end weapons.