Do whichever one you feel comfortable with. Some of us are competitive by nature and would not be satisifed unless we "cut our teeth" in a top tier IM prelim program. Sometimes we feel that our training is not complete without q4 inpatient months, an ICU rotation, etc.
Others of us prefer to take it easy after busting our hump to get into RadOnc and go into a transitional year. Less call, more electives, and less stress in general.
I was in the latter category but wound up in the former.
My take? It doesn't make a damn bit of difference. Do whatever pleases you the most.