This question seems to pop up on whirlpool semi frequently so it is probably worth looking at. The answer is very dependent on your play style, how you want to play, what gametypes you play and how you aim.
A quick recap of heavy barrel and suppressor mechanics.
Reduces ADS spread by a lot
Increases damage drop off start and extends end
Increases vertical recoil
Increases hip fire spread by a lot
Overall this means a weapon with heavy barrel is more accurate and capable dealing damage to a longer range than a weapon with another attachment. The main trade off is vertical recoil which is easily controlled in battlefield 3. There is a reason this is probably the most popular attachment for assault and carbines – its negatives are not very impactful and its pros are excellent. Apparently the original release of bf3 had the HB adding more additional spread to each bullet that left the barrel when bursting. Thus after around 7-8 bullets there was so much spread the player had to stop firing. This was removed but not mentioned in patch notes at the time.
Hides fire actions on the mini map
Slightly reduces vertical recoil
Increases AD spread
Reduces muzzle velocity
Reduces maximum fall off distance
Increases hip fire spread
I whored the suppressor before the first big patch and have hardly touched it since.
Overall the suppressor modifiers are killer. Damage, accuracy reduction through spread and via not using the heavy barrel, shorter effective range. Feels like shooting spit balls. 1-2 additional bullets to kill and you have to lead significantly more due to the massively reduced muzzle velocity and drop.
The largest benefit is hiding you on the mini map.
The problem with heavy barrel
There is no problem, the attachment is too good and leaves little opportunity for variation because of this. DICE stated at one point that the naked weapon should be the benchmark and perform in the middle of attachments, however this is not the case. Because of vertical recoil mechanics the heavy barrels main negative is easily controllable. You can really feel the weapon downgrade when not using the heavy barrel, accuracy is out the window.
So… heavy barrel is the best?
If you had asked me a week ago I would have said yes, however the past 3-4 squad rush games along with some pubbing has made me appreciate the suppressor a little more. For reference I run AEK + foregrip. I have not always been a heavy barrel lover as I used and abused the suppressor until it was nerfed (and heavy barrel buffed) in the first patch.
The main point to note in relation to the ADS spread reduction is that it simply does not matter all that much unless the enemy player is quite a distance away. The spread patterns on symthic for various guns look terrible, however that is at a distance. Up close to around 50m I think the suppressor is most excellent. In squad rush this is compounded by the fact that most teams my clan has played run heavy barrels or flash suppressors. This means it is a little different and throws something else into the mix that they need to deal with and at my teams play level they may not be able to do this in the three sets of a game. For squad rush in a competitive environment I don’t know if it would be viable for a whole team to run suppressors, but one or two people would probably be decent.
You do need to keep a few things in mind – it suits a roaming role better than a stationary role, or if the role is stationary on defence you have a few different peek position options.
There are some situations where I would take always a heavy barrel. For instance on metro. If my job is peeking lockers while attacking I would take heavy barrel. The distance is enough and the encounters very brief – every bullet counts. Hiding your location does not benefit you because that particular encounter is extremely linear and a player is almost always there.
Final word on the suppressor
I have enjoyed it lately, even in competition games that I would usually not use it. It makes it slightly different at at my teams level (not awesome but not crap) I feel one player running it gives us an advantage, if only because the other teams are not used to it.
I would not run one on 64p crowded maps due to so many players in a small area – you are likely to get spotted anyway. I would not run one on the armored kill maps that frequently have long range encounters. I would not run suppressor if you play at a low level for fun – players at this level are not likely to use the mini map as heavily, removing the main reason for running a suppressor.
Finally if you are very accurate you may notice the decrease from the heavy barrel, even at close range.