Generally when you use Savannah Heat, your hoping to wipe people out in a few quick seconds a get an early lead in terms of kills or damage done.
Mind Blast offers sustained damage over a longer period of time as well as the ability to power out utility skills to aid the rest of the team.
MB is good
How ever snare teams in HA like to use SH for really painful dmg it rarely works apperently but still I have seen alot of teams trying it out
Yeah. Having tried both, MB tends to offer better results, as it allows for greater utility (wards, or convert, or extinguish, or aegis) plus some damage (not great, but provides adequate pressure).