The benches for either option would be very tough to overcome, way too little experience.
As for the whole Griffin v Hayward debate, Griffin is easily the more obvious fit from a roster construction view. I am not interested at all in a starting front line of Horford and one of Hayward/Crowder. It's a fine small-ball lineup or closing lineup, but is not sustainable as a starting unit.
But Hayward, to me, has become the better player. Hayward is younger, healthier, and just strikes me as a guy who would be more likely to fit in with the team culture. If Crowder would accept a 6th man role, and we could find someone else (maybe eventually Zizic) to fill the other front court spot next to Horford, I'd prefer Hayward easily.
I can't quite put my finger on the exact reason, but Griffin just seems like an under-achiever. More focused on his own goals than team goals. A bit too "Hollywood" for what the Celtics have been building the last few seasons.
All in all, given the pros and cons of both players, I think I'd prefer Hayward. We'd still have work to do to address the front court, but I'd rather have that problem than go after Griffin, only to see him continually get injured or just not mesh well with the team culture.