Ditto on the 2.0
the 1.5 will have to work harder to Move the same Mass = use more gass, what do the carjam / Trademe Fuel stats say?
Also assuming your referring to these
Third generation (2007–2014) – GE, GV, GH, GR
Sedan (pre-facelift)
Hatch (facelift)
and with zero 1st hand experiance I'm gunna go by the Trademe listings that popped up 1st
both 2008
1.5 : https://www.trademe.co.nz/motors/used-cars/subaru/auction-1861777980.htm?rsqid=da4883b855d04da7a9443669e8e735e5-002
2.0 : https://www.trademe.co.nz/motors/used-cars/subaru/auction-2167677172.htm?rsqid=da4883b855d04da7a9443669e8e735e5-002
all depend on how heavy your foot is I guess & every day you get in a 1.5 you'd wish you went for a 2.0 anyway
also one could spout out "Newer Auto Trans these days are much more efficient than those of the last Millenium a ther ehave been advances in parasitic power losses" etc