Since the most recent built went live, I went ahead and tested both abilities. Here are a few observations of both based on level 87 stats:
Zen Sphere:
Requires two Chi.
Instant Cast.
Tooltip is confusing - As of now, the sphere only goes above the casters head or friendly targets, not enemy targets.
If above a friendly target, it will heal for mid 10,000 each tick (And possibly do damage similar to being casted on yourself).
If above the caster (yourself), it will deal mid 10,000 damage each tick.
If around multiple hostile npc's, it will attack the target you're selecting.
Chi Burst:
Requires two Chi.
.0883 second cast.
Mildly slow travel time
Hits for 13,000~.
Heals for 8,000~.
Tentative Observations:
As they are now, I very much prefer Zen Sphere over Chi Burst. Not only does casting as a melee spec feel klunky, I'm sure it also cancels your auto-attack. Even if that was not the case, the output of Chi Burst which requires a cast time is lackluster compared to a "click and forget" ability like Zen Sphere. As for the healing aspect, Zen Sphere wins in both time cost and effective output.
As a side note, the Chi Burst animation is currently an untextured block. Hurling blocks at mobs is actually quite fun