I've not used the AF versions of either, but have both the 180/2.8 and the 150mm f/4 (schneider) - actually I also have the 150mm apo macro too.
All three are very nice optics. The advantage of the 180 is the faster glass and it indeed is wonderful for portraits. At least on the manual version the focusing action is just a delight - very smooth and its quite easy to hit focus. With single point AF I can't see how much I'd be using the AF feature anyhow. This lens works very well with the 1.4X with very little or no noticeable ding in IQ. If the lens itself is a big large, then the hood can only be referred to as a pig. It's a very thick solid metal piece. I suspect this will hold up more cars and elephants than a phase one back! The hood is my only complaint - the lens has some great properties and fantastic IQ.
The advantage of the 150 is you can get the PQS version for one stop faster sync, and as Graham has already pointed out its much more compact. One other advantage of the 150 is it uses a bay VI mount which means if your other lenses are the 50/4, 60, 80, 120 then you could share the same filters and use the matte box/compendium. I find this a really useful feature. The 150mm tx draws so beautifully... a very nice lens. Pretty flare resistant and super excellent bokeh. I have not used the 150 sonnar (Zeiss) version so can't comment.
the 150 apo macro is different altogether and I haven't shot direct comparisons to the 150 TX but observe they draw differently. Because the 150 apo has to be used with the bellows or extension tube, its more cumbersome.
For portraits in studio - I'd take the 180. For an all around lens - I'd look for the 150 TX.