I'd trade both of them, if other teams were willing to give up future assets (i.e. 1st round pick or similar value).
I like both Crawford and Bradley, but to keep them beyond this season the Celtics are going to need to invest 3+ years and better than MLE money. That makes little sense for a team in a rebuilding phase. Better to sell high on them.
Assuming I have to pick one, and they both cost the same, the decision is not an easy one. It's an interesting question because one guy is a big boon to the offense, while the other is a big boon to the defense. Each is, to some extent, a bit of a detriment on the opposite end, at least compared to the other.
In light of what I said above, I think I'd gauge the trade value of each and then keep the one who is worth less on the trade market.