Both of these texts have recent new editions which are comprehesive, well written, and are vast improvements over the past editions.
Personally, I favor Rockwood and Green. I would recommend picking a couple of chapters (say, tibia fractures, femoral neck fractures, and distal radius fractures), reading those chapters in each text, and then choosing the one you like best.
The one thing Skeletal Trauma has going for it is that the OITE references for trauma always seem to come from there, rather that Rockwood and Green. (Not that you won't find the same info in both books)