Whats the best buffer weight to use in a FA suppressed 9mm?  Its a standard carbine tube.

I'm using the hydraulic 9mm Blitzkrieg/Kynshot buffer.

I'm running mine in full auto in a 9mm CMMG Guard setup.  Running suppressed and un-suppressed.
The Guard is a 'radially' delayed blowback and uses a bolt / carrier arrangement like 556.

The buffer I'm using is designed for straight blowback in a carbine tube which is probably what you are running.

However, I realized this buffer is the same length as an A5 and now run this with other uppers, 9mm, 556, 5.45, etc..
This link goes over several different buffers I tested: 9mm Guard testing
I don't know what your goal is in terms of 'best'.  I want smooth but also want slow enough to pull singles.

I'm not so concerned about slowing it down a ton. It's just a blasting toy, with reliability and smoothness being my primary concern.  How do you like the guard system? Wonder if it would work with a qc10 glock lower setup?

I really like the Guard system.. So much so that it has squashed my desire to get a transferrable MP5.  
I absolutely cannot stand a straight blowback Colt 9mm setup...Ran them for years trying to smooth them out for SMG competitions.
Don't know about the QC10 Glock lowers but a buddy of mine is running a cheap PSA Glock lower with the Guard with no mods other than removing the ejector since the Guard uses the ejector in the bolt like 556

I've been running an Enidine hydraulic buffer for years in my Oly 9mm upper. It smoothes things out and slows the ROF a bit, not MP5 smooth but a big improvement over a regular buffer.

Just ordered a Kynshot to use in a semi build.

I used an AAC Rate Reducing Buffer in my Reg. FA AR9.
Still a little jumpy.

Thanks guys.

I came to the same conclusion.  I was able to get a slow RoF with the AAC buffer back in the day with a regular blow back setup but it was too bouncy.

Fast forward to today with the Guard system... I tried the old AAC buffer with that and while slow it was too bouncy.  Wouldn't lock the bolt back after the last round either.

I posted my buffer testing with the Guard here: http://c3junkie.com/?page_id=538