200s

My training partner and I got into a discussion about training for 200s last night. His view is that you should NOT do repeats of 200s but work on repeats of 100s with short rest intervals. I think that one should train specifically 200s and do moderate to hard sets of 200s with longer rests. He is talking about 15 to 20 seconds rest, and I am thinking about 45 to 60 seconds rest. What is your opinion and what would you suggest? My goal is to swim 200s faster than I am, both free and back. Thanks,