Belinda is still the better witch. She improves all other witches , usually comes cheaper and is free. Besides that , she is plat (aka faster skill usage)
Yuyu requires you getting lucky in a premium draw , and that's not a reliable way of getting units (even gold ones).
Also witches are more reliable then mages , lol , considering u will use mages less often then witches in general.. Also , most maps can be done with literally any mage, or even with a summoner , without that much of a difference. On a side note , range increase witches are needed on some maps if u don't want to have to cc like 3 silver witches in her stead...