I have both a Softie and a Buffalo, and to summarise I use them for slightly different things.
The Softie is great when you need some warmth, normally when not really active (i.e. on stag, or bimbling around on exercise during one of those waiting periods before the rushing periods etc.). It can be easily taken off, stashes small and light, is windproof and warm - as you will be aware!!.
The Buffalo is different - If I am bimbling around outside (not tabbing as it is too warm) and likely to be in and out of vehicles/buildings (warm/cold/warm etc.) I would take the buffalo. It very quickly zips up to be warm, and has huge venting for when you are somewhere hot so you do not sweat your nuts off. It is however a pain as you need to pull it over your head, as it does not zip like a jacket.
I love them both, however if pushed to choose I would go for the Buffalo, because it meets more of my needs for what I do (i.e. can cope better with temperature variation without taking it off and putting it back on). However the Softie is excellent too and if you are not in and out of warm/cold environments it is fine and you can unzip it even if you look a right scruffy cnut. It is very close and both will serve 99% of each others needs.
Get the Icebreaker merino stuff as it doesn't smell when you have worn it for a fair while and if you were to use it on ops it wouldn't burn and stick to you like all the nylon/man made stuff would should you have any unpleasant encounters.