The YRS is a 1.5L. The YR is the 1.3L. YRX is basically a YRS with a bodykit, different wheels and foglights :P
I know ive purchased 3 Yaris's at hail damaged auctions of late and know all the lil ins & outs of the cars...
Gets me is the Sedan version of both YRS / YRX's has the hideous steering wheel that looks plain jane but on the hatch you've the nice steering wheel with audio controls !
Love the YRX rims but other then that id have the YRS overall, in theory if the YRX is the sportier version atleast throw in some decent seats like the MY03 Echo Sportivo's...Another one of my hail purchases