Alright, first things first:
I want more than 7 companions (!) because 7 simply doesn't cut it anymore (too many races IMHO - can't cut any of the Milky Way races we've had along so far (Asari, Turians, Salarians, Quarians and Krogan), you can't have only a single human companion either IMHO (I could do without humans on the team, not that I don't like humans, but most fans wouldn't like that!) and you IMHO need to give us some Andromeda-Aliens, too (more than one), not to mention that most species have more than one gender...also: There's races like the Batarians that should finally get a companion character, too!)
All in all: More than 7 would be great (I'd like a large team like in ME2!)
Note: Unless they want to go the route of giving us temporary companions (you enter some alien races territory and they insist on sending one of their's along, for the time you stay there)...which might be a good addition anyway, even if they enlarge the team (which they IMHO should)
So, what do I want:
- Turian biotic (doesn't need to be female, but that would be a bonus) - biotic because cabals aren't traditional Turian soldiers (so they are more flexible in their strategies, tactics and their thinking!)
- Quarian (also biotic...as biotics are rare in that species...maybe someone who left the fleet because he or she didn't like the conditions there - so not an appologist like Tali (as much as I like her, but I'd not just accept cramped living-space as the norm...as an introvert I need my space!))
- I'd take the Asari from the trailer (but: Damned, get your artists working again and make her look better, not like an overgrown child during puberty and get rid of that smear of dirt around her eyes (what's with that anyway? It did look stupid on Hawke in Dragon Age 2, so why does it show up AGAIN?)....) who hopefully is a great biotic, too (note: Sadly we won't learn more about the ardat-yakshi...they would probably not be selected for such an expedition...I'd have loved to have another as a companion - hell, maybe even help her with her problems...look into a cure etc.)
- Salarian STG operative (more or less like Mordin...though I'd love having a female Salarian along - maybe one who doesn't want to pull the strings behind the scenes...kind of a rebell!) who's into tech (a biotic would be nice, too but as much as I would like a full biotic team, I guess many others wouldn't want that!)
- Batarian hacker (someone who left the hegemony and didn't agree with their policies and ideals (slavery!))
- human female sniper (who plays the Ice-Queen but really isn't)
- human male engineer (soft spoken, but tough when the situation demands it)
As I said, I'd love more, but that's seven already

(I'd love to have an Asari matron/matriarch along who's like Aethyta - headbutting stuff and telling traditionalists to shove off and try new things etc....in essence: Someone rebelling against social and political norms an challenging people!)
greets LAX