If its a 2006 Cat its likely a C7 engine, which can be set for 300, 330 or 350 HP, just by changing the ECU options.
Which engine is better is a question with no answer, just personal opinions. What's more important is which previous owner was more faithful in assuring each fluid & filter change was performed as recommended. I would buy whichever one came with the best maintenance records from the previous owner (assuming there were no other deciding factors in the rest of the rig). An owner that keeps detailed records of all maint performed, is usually an owner that makes sure maint is done on schedule.