I like Omega Bayern for an Oktoberfest. It's supposed to be Augustiner's yeast. It makes a great helles, pilsner, Vienna, bock, etc. but I especially like it in an Oktoberfest. S-189 is very good as is Diamond but I feel like S-189 is just a little bland on the yeast character. I believe it's technically a Swiss yeast but that shouldn't necessarily exclude it. Another good option is 2308.
EDIT: We were posting at the same time. Wyeast 2352 and Omega Bayern are the same strain.