I'd prefer neurotoxin over healing tip.
At best you'd get about 100-300 Hp extra unless u have more than 1 healer in the team.

Why neurotoxin over healing tip

Once enemy(s) immobile u just keep healing each round. free 3 rounds on heal.

Note: that Poison Fog and Shark Bomb can crit also.
I had instantly done immobile 3 units before.