Completely different?? It's not like one is a playmaker and 2nd is a destroyer. Poulsen is primarily a destroyer. Don't let his better passing of the ball fool you, their tasks on the pitch are almost same.
Sissoko distributes the ball a lot if you haven't noticed. But he doesn't do it very good. Hence he looses it often.
Comparing Sissoko and Poulsen is the same as comparing Zanetti to Sissoko.
I don't believe you can do that primarilly because they are players that hae different skills. Kind of like comparing Del piero to Trezeguet. They are both strikers and have more or less the same job on the pitch which is ti put the ball into the back of the net yet we can't compare them because they have completely different styles of play.
It's not about the position of the player as it is his charectaristics and what he does best. Sissoko does not distribute the well, when he does, most of them end up on the touchline. He does make occasional runs into the box, something Poulsen can't do. However, Poulsen has showed us a few times this season that he is capable of distributing those long balls very precisely into the area, kind of like Zanetti.
I don't think we can say one is better than the other, that's just my opinion.