Seraph Armor (Long War)
Seraph Armor incorporates the same jet pack as Archangel Armor, but it trades protection in favor of mobility.
Seraph Armor is a cheaper alternative for achieving an elevation bonus or to facilitate flanking of 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 - you 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.