FYI, we don't use a 3012LF in our cabs, it's a custom OEM that Eminence did for us that I'm really happy with. As far as the mid driver, the 18Sound was never a contender. The ML212 is based on using 2 mids stacked vertically. The 18Sound is both too loud and too expensive to use that way. We also don't use an L-pad on these mid loaded cabinets, instead choosing to use drivers that are well matched for each other. We had been using a Celestion (which is a great sounding driver by the way), but just very recently have decided to switch to the Faital for pretty much the same reasons Ken has noted.
The Faital, to my ears, sounds a little more 'tweeter' like, where the Celestion has a little more "in your face mids". Because the Faital loaded cabinet has a little less going on in the upper mids, it actually gives the entire cabinet a little wider sound. The cab sounds a bit fuller in the deep lows and a bit brighter on top, simply by switching to the Faital. I think this helps the cab not sound so foreign to those players not accustomed to a mid loaded cab. The thing that sold me on the Faital, is the fact that you can get it to sound very similar to the Celestion with just a slight boost of the amps EQ at around 3k. The Celestion, on the other hand, isn't capable of the reproducing the slightly brighter top end detail of the Faital.