The first and most obvious is design - the GTS 2 has a rectangular aluminum body with a 1.65" AMOLED display and 20mm silicone straps. The GTR 2 on the other hand has a round 1.39” AMOLED display and comes in two versions - a Sport edition with 22mm silicone strap and an aluminum body and a Classic edition with stainless steel casing and 22mm leather strap.