Personally, my favorite irons are the RPD/AK47, and the Scar a close second.
 
I use the ACR a lot, and find it's sights are barely usable.
 
I really dislike the irons on the M16, FAL, and the Tar.

The SCAR has an awesome iron sight, and so does the M4A1.

I like the ACR sights compared to any of the rest.  But I hate ALL iron sights so there is no competition between them for me.

" @kenya24: ...And most of the LMG sights are pretty good. "

I think the scar has the best sights, closley followed by the vector.

I only use the RPD and AUG in the LMG class, do they still have that one LMG whose irons take up like half the screen and don't tell you much? I fucking hated those.
 
And yeah, I like the SCAR's and RPD's the best probably.

I think the ACR has hand's down the best iron sights in the game. However, I think all of the iron sights in the game are at least acceptable in comparison to CoD 4 which had some pretty awful ones. 
The only iron sight i find i dislike a lot is the FAMAS.

I love the M16's iron sights, and the UMP.45, i think those are the 2 best in the game. 
But yeah the FAMAS's sight is just horrible, the whole gun just looks nasty as a matter of fact.

SCAR for best sights..still the M16 for the worst

SCAR has easily the best sights and I'd have to say that M4 has the worst. Those sights block like 3/10ths of your screen.

RPD Iron-sights for me!
 
It does it's work and it can basically be used as a sniper rifle it's so accurate.

FAL Iron-sights are the worst by far.
 
AUG Iron-sights are the best for me.

I'm not surprised to see such a wide range of preferences on here. Personally, I don't have any problem with ANY of the guns' iron sights, except for the L86 LMG. In fact, for a few of the guns, like the TAR, I vastly prefer the iron sights to the red dot.

yes, the tar has really good iron sights too.

I can use most iron sights, but FAL is the worst so far.

i love the fal iron sight

I'm totally fine with all the iron sights in this game. Cod4 i couldn't stand iron sights, but in this one i don't mind them at all. Best would probably have to be the famas or scar, but i can't think of any off the top of my head that i don't like.

FAL
When you look to the left or right, the center notch is completely obstructed.

The SCAR-H is really easy with it's iron sight.
 
And the ACR would have to be the hardest.

UMP. Aww yeah.

I HATE the way the SCAR's ironsights look but they are by far the easiest to use. 
RPD is also good because it doesn't block any of your vision.
ACR I don't mind (although I hate the gun itself). 
M16 probably has the worst ironsights in the game imo.

I'm good with the ACR's Sights. 
The FAL however.... Fuck that shit.

RPD
 
Everything else shits me until i get a sight.

I like pretty much all the iron sights - they seem a lot bigger than they were in Call of Duty 4. Still, here are my favorite ones:
 

• TAR-21
• ACR
• UMP .45

I am also partial to the TAR iron sights. I do very well with them

Most LMGs have manageable iron sights. ACRs and M4A1 also have pretty good ironsights. As far as worst go, I'd have to say the M16 or the FAL.

The AUG has nice iron sights

" The AUG has nice iron sights "