I prefer split routines because then I'm getting my heart rate up more than once a week (in your situation). Working all the muscle groups at once would fatigue my body to the point where I'm not operating at full capacity by the time I get to the last muscle group.
I would also not want to wear out my whole body if I did a really hard workout. Sometimes my lower body gets really sore if I haven't done some squats and lunges for a while. I can deal with that alone, but throw some sore arms on top of that, and I wouldn't want to move much the next day.
I'm no expert ... just my two cents.