My first play through is likely going to be a human female rogue. I am thinking that Cullen is the first romance, so that takes LI off the table.
I generally pick my party based on the ones I like the most combined with the ones I need to round out the group.
So, I need 1 warrior, 1 mage, 1 rogue with one open slot.
For warrior, I've really only seen a little of Cassandra and Iron Bull, not so much of Blackwall. Between Cass and Iron Bull, so far I like Cass better.
For rogue, I already know I find Serah's voice to be grating to me, so that sort of puts her out of the mix. I know I like Varric, and I know nothing about Cole. When I run with two rogues, Varric will almost certainly be my choice unless he's changed a lot.
For mage, I was originally thinking that I'd like Solas the most, but Freddie Mercury, er, Dorian is really starting to grow on me, too. Vivienne is still something of a cypher, so she's less likely to wind up in the party at least to start out. Right now, I'm leaning Dorian.
Realistically, I am looking at myself, Dorian, Cass with one slot open to be rotated depending on the situation. Of the cadidates for that slot, Varric may wind up filling it the most as the most utilitarian option as another rogue, but there is always the option to drop in an extra mage (Solas) or warrior (Blackwall/Iron Bull) as the occasion demands.