those are very very different shows..... watch madoka if u want a serious and dark magical girl series with an involving plot. watch precure if you want a fun kids show where they fight goofy monsters (disclaimer: ive seen like three eps of one precure series but i think this is what its generally like, it probably gets semi-serious eventually like sailor moon but probably not anywhere near the level of madoka)
also i think precure series are generally around 50 eps long or so & madoka is 12 eps