Not near my books, but don't Draconic need to spend a sorcery point to get Resist Fire for an hour, while Stormborn have the (lesser used but not unused) lighting and thunder on all the time?
Draconic really wants you to go fire only, and to keep that viable you need to spend a feat. Stormborn choose either damage type as adders, but do it point blank and ally un-friendly.
Stormborn get a lot more spells, but many of them are either (a) partial spell you can't cast with full versatality, (b) don't scale well with level, or (c) aren't spells you would have picked up so it's not freeing up slots. But it is still a lot of slots that can help fill some cases.
Both look very playable. Which is more "powerful" probably comes down to your playstyle and your table's feel.