Personally, I've never thought the Yachtmaster was dressier than a Sub, although I believe as Mimo stated, I think its flashier. IMHO once you are dealing with something that has a rotating divers bezel, its definitely a sports watch. In addition, while I think the steel version with blue dial is handsome, I've never really understood the Yachtmaster's purpose. The Sub is clearly a divers watch, a GMT is a pilots watch or travelers watch, the Daytona a watch for race car drivers etc. The Yachtmaster has never struck me as a true purpose built tool watch.
I wouldn't have any problem pairing a Sub with a suit. I would probably opt to wear a true dress watch for very dressy occasions, but I have seen attorneys, judges, and other business men etc wear Subs with suits in the past and it looks fine. Depending on your work environment and style of dress, a Sub can be a very good daily wearer. Good luck with whatever you choose.