What tranny oil to use

I need to change the oil in my sonatas . but from what I have read online it looks like there is a lot of controversy about what tranny fluid to use. A lot of sites say to only use the Hyundai's sp 3 oil. But a lot of other sites say you can use other brands that say on the bottle that their oil is just like hyundai's sp3. The Hyundai tranny oil is expensive. But if other brands will harm the tranny I will have to buy the sp3. Do you think the other brands that say they are just like sp3 will be ok to us ?.