They both seem to have similar ingredients. Both companies also offer a money back guarantee. So I guess you got nothing to lose trying either one. Except that Euoko is alot more expensive. But I've heard good reviews of both brands.
I haven't tried euoko but i am trying meladerm and to me its helping well, i think the euoko white range is far too expensive whereas meladerm uses similiar ingredients and is at a more reasonable price. Meladerm works so far so good for me, i've only been using it 3 wks now, i am noticing lightening of freckles and melasma that i had on cheeks and chin, looking forward to using it for the next month see what the results are.