avanza has the ground clearance of BRV or ecosport but is narrower and shorter than both mobilio and ertiga. rear wheel drive has its advantages but is less fuel-efficient than FWD. the avanzas that are priced competitively w/ mobilio have just 1.3 engines while the mobilio has 1.5
ertiga and mobilio have similar size and ground clearance but while mobilio is priced a bit higher, it has more powerful engine.
as for exterior styling i'd have to give it to ertiga. avanza is downright ugly. mobilio's front has improved a lot since the facelift
reliability. you can't go wrong w/ honda. cant say the same w/ the daihatsu avanza or the maruti ertiga but i'm sure they have pretty good reliability too, just not up to honda standards
take note what i said only makes sense for the M/T versions coz that's what i'm researching on right now