At first, I was quite pleased with Samsung based ROMs as I (mistakenly as it turns out) thought that multi-window, S-Voice, keyboard, camera and SPlanner were more refined than Google's effort. How wrong I have been. I have returned to the true Android world again, having briefly flirted with Samsung based ROMS (always custom I may add and those have been for the most part much better than stock), having come from a Galaxy Nexus that never used anything else but custom JB firmware and really like using my S3 again.
I am using Sentinel 4.40 ROM with a Yank v1.5 Kernel and this thing is flying like never before. No contacts lag, no battery drain, other than what one could consider fair and reasonable, no S-Voice that never recognises what I'm saying, no b****y multi-windows that I never use anyway (what's the point when you have multi-tasking natively anyway) and Splanner, which is much better than Google's stock calendar I have found a sweet alternative for, better than both afore-mentioned, IMHO.
This is how this device can perform without all Samsung's 'baggage' that, if we're honest, very few of us, very rarely ever use. One final word of caution, the CM10.1 based ROMs all seem to have a problem with the Cameras. In my case it was the video recording, which worked but without sound. Having done some searching I found a 4.2 based zip over at XDA Developers, which has done the trick and now everything, and I mean everything (including WiFi AP, Bluetooth, NFC) works.
One final note, the thing I found really useful on Sammy based custom ROMs, at least the ones I was using, was the in-call recording function. But even for that purpose I found a sweet and fully functional alternative.