You may want to do both.
The foam will change how the fly works in the water by adding bouyancy at he tail. This can be good or not so good, depending on how you work the fly.
The marabou tail will not add bouyancy, but will add 'action' as it pulses and flares each time you move then stop the fly.
So, perhaps if you are 'hopping' the fly along the bottom with short pulls and long pauses, the foam tail will wave seductively in the water. If, instead, you are using a faster or more steady retrieve, then the marabou pulsing and flaring as you move the fly may be more productive.
By the way, the needle technique is how you put on the marabou. Also add a small drop of CA glue, because when you pull the needle, it puts some slack in the wraps....without it, the marabou will come out on the back/false casts.
It Just Doesn't Matter....