There are alot of different reasons, but use each one according to your play style. I use Fleet Foot when I'm playing offensively and aggressively. On the other hand, Cloaked is more suited on a defensive person on Team Objective. It is usually used when someone is trying to do the objective. Well, hope this helps!
In my opinion, I beileive fleet foot is more effective since you can move significantly more faster with objects like propane tanks, and riot sheild. Cloaked is a good booster to be chosen in game types such as Elimination, Team Objective, and/or Lab Maps. So, it depends on which game type you are playing.
Well a best loadout is Fleet Foot Team Safe an sniper/mega bomb use on your carachter one hat with cloaked for example Chloe Frazer and you will have cloaked on level 1 i think and fleet foot on level 3! Hope you Enjoy!