roshi is slightly better specially if you have more power and initiative than your opponent and deals way more damage than han.,but can go down pretty fast if u dont have the support to keep him a live for a few rounds and works pretty much with all elements. Han is the destroyer of blitz and a better tank than roshi,but only shines with either fire main or water main since these are the only 2 classes that deal damage with dots and don't rely on buffs.

so if you have mei and you're either water or fire main go for han.If you don't have mei or roshi,and you're not a fire or water main go for roshi.