There is no best healer. Right now whm and sch seem really on par. Just sch still is the stronger single target healer and whm still the better aoe healer. Both are great choices.

However astro is for the most part in need of some tuning.

Currently it has the most MP issues. Weakest heals, few emergency heals and cards are weak and unreliable. The sch Fairey Selene buffs party dps more then the astro cards can currently.

Most party's that are trying to set up savage statics are looking for the whm + sch wombo combo.