For new sylphs upcoming after the patch, here's a quick bit of information:
1. They're free.
2. If you are using a Will Destroyer Astral (you shouldn't), get the fire sylph.
3. If you are using a crit build (you should), get the lightning sylph.
4. Mages may want the fire sylph, but archers and knights probably won't.
5. The lightning sylph does matk, the fire sylph does patk.
6. Yes, they are vastly better, against single targets, than Apollo. However, Apollo does more overall damage to multiple targets.
7. The passives on the new sylphs are atk bonuses.