As someone who had a cold and had to miss my time at the dojo monday night (my only solace from a viscious pregnant wife) I say that it is best not to go to class.
Besides getting someone else sick during all those throws and pins (infected sweat drippin' everywhere) having a fever or being too tired could result in injury. A simple breakfall, done incorrectly, could result in a bad bruise or worse...
I tried going back to class last night (still gettin' over the cold, but I felt well enough) and had to sit out a bit but it was good to be back. Maybe there should have been a fourth option such as : Go to class but sit and watch?