It depends on how many days you have there and how many days you can make rope drop at DL. Whether you do Nemo on an MM day or non-MM day, if you do it first there will be lots of people heading that direction. The rationale for doing Nemo during MM was that there were just less people there for MM than for a regular opening, and hence it was easier to get to Nemo on such mornings. The other choice for MM - Fantasyland - will be roughly the same whether you do it during MM or first thing on a non-MM day. That is why I chose to do Nemo during MM.
However, we are now coming up to year #2 of Nemo subs and, as others have said, lines are not as long especially in the evening. If it was me I would probably still do Nemo during MM and then Fantasyland on a non-MM morning. But then once thru Fantasyland is enough for us because our kids are older.