Whatever faction you want to get the item from. They are all the same stats wise (29 to all stats), only difference is the exotic gives a buff to whatever faction you got the exotic from, and they give a different effect to your ghost upon death.
For instance if you did the Dead Orbit one, you would get a buff to faction gains to Dead Orbit, and a Dead orbit effect to your ghost.
Biggest perk with getting that exotic is raising your light level super quick. It would allow you to have one 280 year one exotic armor piece that you ascend, and one 290 class item armor piece. With another 280 year 1 exotic weapon also ascended.
For instance this is the Dead Orbit Warlock one
https://www.bungie.net/en/Armory/Det...ht%20Beyond%22