Parkin is hardly one for the future, hes very well proven in League 1 and had he not got injured would probably have banged quite a few in for Ipswich in the Championship last season.
id go for Parkin personally.
Age being the major factor, still has things too prove etc.
Horsfield may be the better player at the moment but isnt going to improve where as there is plenty more to come from Parkin in my view.