I was assuming that the reason for using true mountaineering boots was that they will readily accept the 3 types of crampons - hinged, semi-rigid and rigid while the winter boots mentioned often do not or do not well.
If by "true mountaineering boots" you mean plastic doubles, there are pros and cons to them. (Or "advantages and limitations" as my BSA climbing director likes to say...
)
PROS
-stiff sole (good for cramponing and esp. for vertical ice)
-removable liners can be kept warm in your sleeping bag overnight
-waterproof (as in: boot material won't get soaked like leather boots do, not as in: will keep your feet dry if you punch through during a stream crossing
-oftentimes warmer than a single boot
-will take any type of crampon (hinged, semi-rigid, rigid)
-will accept any type of crampon binding (strap-on, semi-automatic, step-in)
CONS
-stiff sole (bad for long approaches/hikes, esp. over broken terrain)
-tend to be heavier
-bulkier (bigger boot volume for a given shoe size)
-can result in shin bang and/or toe bang
-more expensive (generally)
It really comes down to what YOU want to hike/climb that will determine what kind of boots to get, and even for the same objective, there are often multiple options. To wit: I believe Doug (cbcbd) hikes out west in singles, even on overnights, and just puts his entire boots in his bag overnight, where I would be wearing my doubles, leaving the shells in the tent vestibule and just putting the liners in the bag.
I was a big fan of my Asolo doubles for ice climbing, multi-day winter outings and even for day hikes in the ADKs and Whites. Then I picked up a pair of single, synthetic ice climbing boots (also happening to be Asolo's). OMFG they are soooo much more comfortable to hike in!! They are about half the weight of the doubles and MUCH more flexible. Going forward I'll be wearing these for day hikes and ice climbing and only pull out the doubles for multi-day trips.
I concur with the advice given upthread: get boots that are WARM, regardless of style (single/double). Also, TRY ON as many boots as possible --
wearing the sock/socks that you will be hiking in -- before making your purchase. Unlike a lot of other hiking/climbing gear, boots are not the ideal thing to buy sight unseen over the Interwebs. Each mfg uses their own last(s) and will have a different fit. Your preferred size in Koflachs may very well be different in Scarpas, which may yet be different again in La Sportivas or Merrills or Columbias or Asolos.
The good news is that there are a LOT of good boots out there these days. You just need to find the ones that fit. Fit your needs and fit your feet!