All of them are really good. And the usefulness of each selection will depend on each characters. But I like the Heart most.
Heart ... Breath weapon's damage is not that great. But you can easily add another die with a cheap magic item (Dragon Spirit Cincture ;2,000 gp; MIC). As you can choose energy type on the fly, it is a good additional combat option for a warrior type. Entangling Exhalation feat makes it even better.
Mind ... Very good for many PCs. Low-Light and Darkvision are useful, especially for casters. But both of them can be gained relatively easily through spells and magic items. Blind-sense is great, though. But I like Warforged as the base-race of Dragonborn and thus it is already immune to Paralysis and Sleep. That is the reason why I like Heart over Mind.
Wings ... Flight at L6 is useful even if that is slow and has round limit. That is still useful at higher level as EX ability. Cannot be dispelled. Works in anti-magic field. You can achieve the same ability with appropriate feats. But feats are precious.