1 hour of intense exercise (minimal breaks) >>> 3 hours of exercise with a ton of breaks and loitering around.
There's a lot of literature that workouts beyond an hour-hour and a half don't add much benefits and the shorter and more intense they are, the better. (of course this does not apply to athletes)
You can even cut that hour down to 30 minutes of high intensity, 'bursty' exercise with no breaks. Art de Vany talks about this in Evolutionary Fitness.
thats what I do. Wake up 7, gym till 8:30, then work with break for food once every 2 hours for 5 minutes (plus bigger dish at evening) then from 10 to 11 cardio, sleep before 12. I do not exercise over the weekends, let body sleep longer, rest, be lazy. If I manage my time properly, I still easily get 10 hours of work a day! I just noticed how much detracting certain things are: talking 5 times about the same thing over the phone with friend, watching TV "only" for couple minutes, browsing web, reading emails that I know I will come back to again later on, etc. It all adds up substantially. The only spoil other than energy drink with 30g of sugar (my daily rate) I let myself to do is to "waste" time here and there on reading HN :)
Exercise definitely. I've found that many of my best ideas come to me while exercising. I don't listen to music or anything so it is the most (sometimes only) distraction free time of my day.
I've also found that, by bike commuting, I can integrate exercise into my day in a way that doesn't really take much additional time.
