Ooh that's a tough one. I would need to recommend Engineering Team if you're fighting against the iconians due to their constant disables.
The other two however are both excellent choices. If you want a fast blob of hull healing with some resistance, go for Aux to SIF. This power is good for enemies that hit you hard. You can also spam this power since it only has a 15 second cooldown.
If you don't mind travelling at full throttle most of the time, Hold Together is definitely for you. At >75% throttle, it will also cleanse debuffs and functions like a lower grade Hazard Emitters.
First and foremost, Engineering Team II. It repairs a good amount of hull. More importantly, it's needed to clear certain debuffs. This is VERY important when fighting Heralds.
For the second one, between ASIF and Hold Together, that depends. ASIF grants a temporary resist boost as well as a small hull repair. Hold Together performs better on higher throttles in its repairs which is a Heal Over Time. It can clear a hazard at high throttles. A reminder also there's a massive difference on requirements of high throttle settings compared to high/max speed.
With those parameters, depending on the ship, build, playstyle, it's really up to you.
If you're flying the T6 HEC at full throttle anyways, then Hold Together would be superior to ASIF but never to Engineering Team, IMO. If you're running, IIRC, the 3 piece HEC set, that has a CD reduction of 15% to Pilot Abilities.
The first two have very different attributes and uses.
ET gives a flat heal and repairs subsystems. Its reactive, so you hit it after taking dmg. Can be enhanced with doffs to reduce cd.
Aux2Sif scales with aux power (at medium aux the heal is about equal to ET) and gives next to heal also DR. The additional resistances give it a proactive use (with 10 of 15s uptime just chain it), if you can fire it before/during taking dmg you could add the mitigated dmg to it heal performance far outperforming ET then.
low aux power -> get ET
need subsystem repair -> get ET
med-high aux power (and no other interfering Aux2something) -> get Aux2Sif
Hold together I just recently started to use. It has the longest cd but also comes with a big DR buff plus cleanse at full throttle. So used at the right time I'd guess its a very strong one.
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The other two however are both excellent choices. If you want a fast blob of hull healing with some resistance, go for Aux to SIF. This power is good for enemies that hit you hard. You can also spam this power since it only has a 15 second cooldown.
If you don't mind travelling at full throttle most of the time, Hold Together is definitely for you. At >75% throttle, it will also cleanse debuffs and functions like a lower grade Hazard Emitters.
For the second one, between ASIF and Hold Together, that depends. ASIF grants a temporary resist boost as well as a small hull repair. Hold Together performs better on higher throttles in its repairs which is a Heal Over Time. It can clear a hazard at high throttles. A reminder also there's a massive difference on requirements of high throttle settings compared to high/max speed.
With those parameters, depending on the ship, build, playstyle, it's really up to you.
Sounds like ET2 is a definite, and it's a coin flip/matter of taste between the other two?
ET gives a flat heal and repairs subsystems. Its reactive, so you hit it after taking dmg. Can be enhanced with doffs to reduce cd.
Aux2Sif scales with aux power (at medium aux the heal is about equal to ET) and gives next to heal also DR. The additional resistances give it a proactive use (with 10 of 15s uptime just chain it), if you can fire it before/during taking dmg you could add the mitigated dmg to it heal performance far outperforming ET then.
low aux power -> get ET
need subsystem repair -> get ET
med-high aux power (and no other interfering Aux2something) -> get Aux2Sif
Hold together I just recently started to use. It has the longest cd but also comes with a big DR buff plus cleanse at full throttle. So used at the right time I'd guess its a very strong one.