No one can say what is the best gun for someone else.
It just takes practice with each gun and such.
But there is a way to try out guns without having to spend your precious COD points.
Just enter combat training.
Make the difficulty "recruit" and setup a game of team deathmatch and 9 enemies against just you.
This will give you tons of XP and COD points in combat training.
It took me about 2 hours to get to level 25 with this.
Once you unlock the gun and have the COD points, just buy it from combat training.
Use it and figure out if you like it, then go back to the real game and buy it if you wish.
I did this after prestiging once
and I regret it.
I would've got to first prestige much faster if I had known what guns would work for me and what wouldn't.
(same goes for perks and equipment and such)
gaming.stackexchange.com/users/138/Earlz
You could play several rounds of the Sharpshooter Wager Match mode and make a note of any weapons you like.
If you play in low buy in rounds it shouldn't cost you very much at all and if you do well you may come out better off.
gaming.stackexchange.com/users/1169/Daniel Ballinger
You could always just run around playing with the default guns for a few days, then go into your stats and see what guns kill you the most.
Chances are people are a little more efficient with those guns, or they're just popular, but they're probably popular for a reason.
gaming.stackexchange.com/users/5145/blesh
To find what guns suit you, go onto split-screen.
From there all weapons, camos - anything unlockable - is usable.
These, however, don't carry over to the multiplayer.
You won't really be able to test them out properly unless you have another person with you, but you'll be able to check out if you want to spend money on the camos and stuff, as well as get a feel for the weapon (e.g recoil).
gaming.stackexchange.com/users/None/
Another great way to 'try out' guns is to set a class that has scavenger, what ever tier 2 and 3 perks you like, and pick up guns from people you kill.
This way you can try out the guns in real combat, though it might take you a bit longer to do so.
gaming.stackexchange.com/users/320/Ritwik Bose
go to system link match.
create game.
and all the options are there
gaming.stackexchange.com/users/None/
I am just starting out and it's expensive to buy guns just to find out that I dislike them. Where can I test weapons in  Call of Duty: Black Ops ?
Is it possible to "try out" guns?
gaming.stackexchange.com
<call-of-duty-black-ops>
gaming.stackexchange.com/questions/12635
gaming.stackexchange.com/users/138/Earlz
You can enter combat training or play rounds of Sharpshooter Wager Match and make a note of weapons you like. Combat training mode is your best bet. You can of course just play a few normal rounds of the game and see what you like or take notes. Another option is split screen mode. 
User suggests combat training mode. Users suggest playing rounds of the normal game and taking notes. Users suggest using split screen mode.