Seraphim Armor (Long War)
Seraphim Armor incorporates the same jet pack as Archangel Armor, but it trades protection in favor of mobility.
Seraphim Armor is a cheaper of achieving an Elevation bonus or flanking adversaries. Combined with perks like Tactical Sense and Damn Good Ground it can make your soldier very hard to hit. Flying also has another advantage - your are far away from melee and grenade range.
If you are considering using flying armor on a regular basis, remember to research the Advanced Flight Foundry project.