Now I am going to expose my "teaching in a STEM field at a major research university privilege." 2/2 is the nominal teaching load, which is in practice reduced to 1/2 or 1/1 for active researchers depending on department policies and buyout requirements. Most research active faculty in my and related disciplines teach one course per semester most of the time. When looking at the teaching preferences of my colleagues, it appears that most like to teach TuTh, i.e. twice a week, because then the other three days are free of teaching obligations. I appear to be in the minority with my preference for MWF classes.
When I was a wee assistant professor, I taught twice a week but then realized it's not my cup of tea. I do the chalk-and-talk teaching with an occasional slide if I need to show something specific; this means that most of the time it's literally just me with a piece of chalk in front of the board, no notes, talking directly to the class, drawing, writing, probing student understanding with my questions and answering theirs. This is essentially a performance that takes considerable focus, which I have no problem maintaining for 50 min. But, when I teach 75-min classes, I find that the last 15 min or so I am neither as focused as I need to be, nor are the students paying attention as well as they do early in the class. So, to me, the 75-min lecture is not a good use of class time overall. I cover more material and do it more efficiently when I teach in 50-min chunks.
Another consideration is travel -- if I have to miss a 50-min class, the loss is not too devastating. They are also easier to schedule make-up if need be because they are short, and because everyone else seems to jam-pack the students' Tuesdays and Thursdays. Also, with a MWF schedule, I can pretty much get any time of day I like because these days are not as in demand.
But, teaching MWF does infringe upon three out of the five work days, and classes tend to fragment your day which is not the best thing for doing research. So I do understand this important criterion that most of my colleagues make when choosing their teaching schedule. Some also say that travel is easier with a TuTh schedule because they can give talks at other institutions on Mondays or Fridays and still not miss classes.
When teaching more than one course per semester, which faculty in my department occasionally have to do, I am still undecided on whether it is better to have one course MWF and another TuTh, or teach both courses on the same days (MWF only or TuTh only). The former makes it easier on any given day but eats up a bit of each weekday, whereas the latter is really quite exhausting.
Do you prefer MWF or TuTh teaching and why? If you teach more than one course per semester, how would you ideally like them scheduled? All on the same days or spread throughout the week?
* A bloggy friend at an institution with a quarter system says that he typically teaches 3 or 4 unit courses, with 1 unit being roughly 50 min.