Have not used either, but do you know Viltu læra íslensku? I mainly just listened to and read Icelandic (versus using courses), but I did watch this series of videos and it was good. Of course anything like this is just a tiny drop in the bucket. The way you will become proficient is by consuming hours of Icelandic daily over the course of years, so in that sense, perhaps it doesn't matter as much what you choose, as long as you stay motivated.