I think arguments can be made for any of the Blue creatures. If you want to be especially defensive and let your fliers take over the game you could pick Wall of Frost to hold the ground against Green fat while you fly over head. Seacoast Drake also makes a great early defender but can also contribute to your air force. Trained Condor is the most aggressive of the cards but almost all your creatures that can attack right now already have evasion. Condor is best in other color combos where the evasion is more limited in the other color. In terms of pick order I'd go:
Seacost Drake > Wall of Frost > Trained Condor
Drake can shift between offense and defense the best (though it is more a defensive card than an offensive card). It is also the cheapest of your options (can never be too early to be curve conscious) and costs only one Blue in its CMC to cast. Wall of Frost is by far the best defender of these cards and will probably be the best of the three in a Green matchup. This early though and with more flexible options left in the pack, I think I'd err towards the Drake. I feel Wall of Frost is also more likely to table of the three blue creatures present as it tends to be a bit underrated. Trained Condor is good but for the cards you already have I think it contributes the least additional utility.
I went Condor because I thought it had the most upside with cards like Scroll Thief and Water Servant, but I only ended up grabbing one Servant and no Thieves. Given how the matches played out I think Wall of Frost would have been best, which I'm finding myself thinking a lot lately. I don't think it's a high pick, but it's a nasty ground blocker, which is a very useful attribute to have in blue/white fliers.
Anyway, I ended up going 2-1 with this deck in a Swiss. I think out of the last 20 Core set Swiss drafts I've done, I've 2-1'd at least sixteen of them. Probably more. I remember a 3-0 and 2 1-2s.
Round 1 was the closest I think I'm going to see anyone get to pulling off the lifegain/Bogbrew deck. They had multiple Newts+Cauldrons, Sanguine Blood, bunch of tertiary stuff like Divine Favor and Mark of the Vampire. Didn't see a Angelic Accord but I figured he or she had to have gotten one. Sanguine Blood got me good game one, game two was a slog versus double Cauldron sacrifices holding off basically all of my good creatures for a few turns, and game three I ranched him with Charging Griffin into Air Servant.
Round 2 was pretty close, and I feel like if I'd played tighter I might have won. He had a solid, aggressive RB deck with nice removal in Geyser and Doom Blade. He ended up winning 2-1 in a close one, and I'm probably going to go back and watch the replay to see if I could have played it differently. This is the match where I think Wall of Frost would have been massively better than Condor. He beat me game three with multiple 2 drops beating on the ground, and life totals were pretty even the whole game. Wall of Frost could have held the fort just a bit more for me to get an extra hit or two in and pull it out, I think.
Round 3 I destroyed a bad blue/red deck who liked to scoop way earlier than they should have. Not complaining.