I honestly can't decide what species I want to play. There are so many possible ways for this play out.
For the record, as I said, I do have a plot in mind. But, as with all of my RPs, I only create the key events. I let the players drive the story between the events and decide exactly how the events play out. I just build the story around what happens. Leaves room for lots of surprises - even for me.
Hm... maybe an Asari Spectre. That'd be interesting.