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)
It depends entirely on their use, and your strategy.
While Hardcore players generally rely heavily on sound, the sound of decoys are far too obvious. As well, with no radar, you might actually confuse your own teammates.
However, if you don't use ghost, then a decoy is a nice way to add a little chaos during a spy plane. Since radar is so rare, many hardcore players literally stare at it as soon as it pops up, and don't think their actions through. You can bait the fire for a coupke easy kills if you keep moving.
You can also use decoys on tactical game modes if planned correctly. It takes a couple moments to realize the fire is a decoy, so If one team mate throws a decoy on the east side of a flag it may open an opportunity to sweep in from the west, clear the area, and steal the flag.
Even if they dont work, their fire is noisy and makes it harder to listen for footsteps and real gunfire, so even against experienced players it isnt a total waste.
In the end, it depends on the team you are playing. I usually keep one extra class on the side with decoys, and try them once or twice to see if they work. Experienced players ignore them, but it covers your real fire. Inexperienced players eat them up, and you reap serious rewards as they run madly around searching. Your milage may vary :)
Best Answer
I've had some really good gameplay in confined spaces where you can spray and pray. I use scavenger pro, steady aim pro, marathon pro with radar equipment and it usually works pretty well. They are pretty worthless for medium to far range, so that's why people probably don't use them.