Tier 1 - Potential pack one, pick one:
1. Trained Condor
2. Time Ebb
Trained Condor may not be a factor in constructed situations, but in limited, it feels like one of the best cards to start with. Time Ebb undermines your opponent's tempo and is fairly splashable. Any deck can use it. Claustrophobia isn't at all splashable, but beckons you into blue with how powerful it is.
Tier 2 - Potential pick one in pack two or three, after my colors are established:
4. Nephalia Seakite
7. Essence Scatter
Nephalia Seakite is a good card; flash is really valuable in blue decks, because it lets you keep up mana for counterspells without missing opportunities to play creatures. Disperse is Unsummon-plus, but that extra mana knocks it down a peg for me. James's favorite card in every set is Archaeomancer; while I'm not quite as enamored, it's very useful and very blue. Essence Scatter is the "Blu-oom Blade," arguably the best piece of removal in blue. Once you're going blue, you're always happy to take it, any pick.
Tier 3 - Solid cards to fill out the color:
9. Messenger Drake
11. Scroll Thief
12. Sensory Deprivation
I'll never understand why Cancel gets shrugged aside so often in limited. If Counterspell were reprinted, it'd be hated as far too powerful, but adding another colorless mana suddenly makes the card unplayable? I don't get it. Messenger Drake is a non-bomb bomb; a 3/3 with evasion and an on-death bonus has a place in every blue deck. Divination is Divination. I never really like choosing Scroll Thief for my deck, but he seems to always get work done. Sensory Deprivation, I don't know, maybe I like it more than I should, but it honestly seems like it can be as useful as Pacifism in plenty of circumstances.
Tier 4 - Not exciting, but playable cards in color:
14. Seacoast Drake
15. Coral Merfolk
16. Frost Breath
In this set, with all the useful enchantments, I'm more willing to main-deck Negate. Seacoast Drake is fine, defensive, helps you prolong the game. Playing Coral Merfolk makes you realize how much more important power is than toughness in low drops. Frost Breath fits into blue decks, but there are plenty of other cards that I'd put above it.
Tier 5 - Cards I have a hard time seeing myself play:
17. Armored Cancrix
18. Zephyr Charge
19. Merfolk Spy
20. Tome Scour
Armored Cancrix can fill out a deck if you really need some depth and defense, but I'll try to find a thousand other ways to fill that need. Zephyr Charge is one of those cards that looks useful, but when the cards are on the table, you'd rather have almost anything else in your hand. Merfolk Spy is a mostly useless 1/1, though I suppose it's better than a completely useless 1/1. I'm glad Tome Scour will be back in Standard, but the mill deck is a tall order in M14 limited unless you get awfully lucky.