Pack 1, Pick 2
The Picks So Far:
Honestly, I don't think Juggernaut is even in the discussion here. Yes, the card is colorless, but both Adeliz, the Cinder Wind and Fight with Fire are just too much better than the card in this format. So Pack 1, Pick 1, I would take either of the other uncommons over it. Which means I'm definitely not taking Juggernaut Pack 1, Pick 2!
If Naban were some random blue card, I think this pick would handily go to Fight with Fire, however Naban is a strong incentive to play U/R and passing Adeliz risks putting somebody else downstream into that archetype. And, to be honest, it's not clear whether Adeliz or Fight with Fire is better assuming the U/R archetype. There are aggressive versions of Wizards where Adeliz takes the cake and more controlling versions where Fight with Fire is almost certainly better. And Naban happily goes into both decks.
I'm going to take Fight with Fire on the tie-breaker that I may end up abandoning Naban, as it's possible the person passing to me is U/R and the Wizard Synergies dry up. But regardless of the deck I end up in, I can potentially splash Fight with Fire. So, while there's a chance that passing Adeliz makes my draft more difficult in Pack 2, I'm more likely to play Fight with Fire and it could still be better than Adeliz in a U/R deck.
Pack 1, Pick 3
The Picks So Far:
If they were the only choices in this pack, I would take On Serra's Wings. While a U/G deck splashing Fight with Fire is a potential option and a R/G kicker deck would love Llanowar Elves, I think it's better to take the card with higher upside that can still be played in the ideal direction of U/R. Controlling versions of the U/R decks in this format often want one or two copies of Cold-Water Snapper and splashing On Serra's Wings in those decks is very potent, especially because they often have cards like Opt and Divination, which both makes splashing easier and helps assemble the flying Turtle combo!
In terms of the on-color cards, we see Academy Drake and Run Amok. I think the world started too high on Academy Drake and still hasn't particularly calmed down. The card is pretty much filler and it ends up in the sideboard of my blue decks more than 50% of the time. Wind Drake doesn't cut it in Limited anymore and seven mana is just too much for a 4/4 flier. It's not embarrassing if you must play the card, but it's unexciting.
If I had to take an on-color card, it would be Run Amok. I'm of the opinion that the best decks in this format are either defined by Run Amok or Divination. Run Amok is surprisingly close to the card Searing Blaze if you end up in an aggressive deck and I often do well with decks that have multiples.
The real decision here is between Run Amok and On Serra's Wings. As per my last explanation, is this deck more likely to be a Divination deck or a Run Amok deck? The Divination-style deck would much prefer the Wings and the aggressive U/R decks would prefer the combat trick.
If I had started off this draft with Adeliz, I think this pick would be closer, as Adeliz can facilitate an extremely potent aggressive deck where Run Amok can be quite brutal. However, with Fight with Fire in the pool, I would rather bias towards a deck that can reliably kick the card (which actually happens more than you would think in U/R, thanks to Divinations and Vodalian Arcanist).
Therefore, I would take the Aura, On Serra's Wings!