I don't know the type of attic you have but most are not insulated like other parts of the house also most don't climate control their attic. So you might have to deal with temperature fluctuating allot more up their.
Attic grows are tough and quite often costly to set up. Mostly due to the extreme heat in the summer months and cold in the winter months. Do a search for attic grows in the indoor section. I remember one guy whose attic grow set up cost him around $1500 or so. I would look for a strain that handles hot/dry enviroment better for summer grows in an attic and a strain that can handle cold/humid enviroment for winter grows.
If you are a first timer or are quite new to the game then go for the afghan as it will put up with a bit more punishment. But if you are feeling a bit more adventurous then go for the Skywalker as imho it is Dutch Passions best strain.