Depends on the person playing
If you know what you’re doing, Fervent is always going to be better. Just gotta play your cards right and maybe get a little lucky.
However, if you are not too sure what you’re doing or can’t make accurate threat assessments, Stalker is your best friend. Just stick to the shadows and pressure.
Fervent when played correctly can be devastating, no need to down players when you can simply run their resources down by heavily damaging them. They’ll be white skulls by the time the mission is done too. Again, it requires accurate and fast threat assessment