3" DP for sure...

As for the whole exhaust, depends on what you do honestly.

When I had 3" DP, 2.5" exh, no cat, no res, stock Y, and mufflers it had a lot of rasp and a little bit of drone. When I went with 3"DP, 3" Exh, no cat, no res, custom 2.25" Y, stock mufflers... I have zero drone and most of the rasp has gone away. Sounds a bit deeper than before. Well worth it for sound and comfort for me....