Can someone help me out and explain why I should buy the BCM over AIMs offerings?  Thanks

BCM = know quality

nothing wrong with AIM for the money (but for $100 I would buy a Tool Craft BCG)

Usually you have BCM which is HPT, MP, C158, shot premed, etc. Phosphate and chrome lined carrier. Good staking. Spec bolts on key.

AI'M is usually no testing or MPT only, 9130 bolt, sometimes it's nitride only to save weight, sometimes, coated with nickel boron.

AIM's bcg offerings include C158 bolts, nitride/phosphate/NiB coatings/treatments, shot peened & MPI. There is some controversy as to whether HPT does more harm than good.
http://www.aimsurplus.com/catalog.aspx?groupid=723&name=Bolts+%26+Bolt+Carrier+Groups

Tomac

I have heard the toolcraft BCG is a good one, but I have no idea where to get one. Any ideas?

http://wcarmory.com/

or

http://www.crypticcoatings.com/coated-bolt-carrier-group/
If you want HPT and MPI.  You can get also get phosphate or exotic coatings.

 
Just look them up on google.  It's been reported that they make the PSA premium BCG as well.  


As for the BCM, they are always my first choice for BCG's.  Most don't know that their BCG was really were BCM first developed their reputation.  Before their KMR rails, before their LPK's and Lowers.  Even before BCM only had two of their own upper receivers (and the logo was on the other side).  It was their BCG that solidified their reputation.  


Back then, there were few true mil-spec BCG's.  Colt of course, but on the civilian side they were selling AR15 BCG rather than M16 BCG.  LMT were occasionally available.  Other Mfg's were cutting corners.  Poor or no staking, poor quality extractor springs. Bolts that were not shot peened or MPI'd.  Shit quality screws on the carrier keys.  


It's well known that many contractors sourced BCM BCG's, and many in the SF community as well.  


So things have really improved over the years, and now there are many great choices.  I won't claim I only have BCM BCG's, but they are definitely my favorite.  They are the ones I have the most trust in.

Out of stock@WC and phosphate & nitride are also OOS @ cryptic.




Anybody tried one of the faxon ones?

BCM does not manufacture any products. They sell you a bolt they purchased the same as PSA or Cheaper Then Dirt.
A high quality BCG with 158 bolt cost under $80. to manufacture. Spend your money wisely or spend it on laser engraving.

This! It's effective marketing and anecdotal evidence for the most part. PSA, Spikes, Toolcraft, AIM wil do the trick just as well.

The newer BCM carriers are top notch. I have two, one I bought years ago when they first came out that did not have the BCM logo, and one about 2 years ago with the logo. The old one is a little rough in the machining department, and it had a small burr on the back side of the bolt carrier that I needed to smooth out after I found it chewing up the buffer. Other than that it has worked just fine. I have one of the AIM NIB M16 BCGs and it is very nice, and I have not seen anything wrong with it so far in my .300BLK upper.



In the past I have always preferred LMT M16 BCGs. I have 5 of them and all have been great. I like their undercut/relieved lug design.



I just ordered one of Brownell's M16 BCG's that I plan on using in a basic range blaster I am putting together. It will be interesting to see how it looks in fit and finish as well as how it holds up after some rounds fired.

I like BCM BCGs...side by side they are nicer than AIM, Spikes and Daniel Defense.

Now the real  hard decision would be one BCM BCG or two AIM NIB BCGs for about the same cost.

Welcome to the election year.  

Please enlighten us as to how they are "nicer"...

Maybe I'm misreading your post but it seems to imply that 9310 bolts are inferior to C158?

 
The thing with 9130 is that for it to be equal or superior to c158, the heat treating has to be done correctly.  Unfortunately, during the last panic, there were quite a few reports of them breaking at very low round counts.  That's turned many of us to sceptics.