For me it's Mao chan.

It's a mystery why Manaha chan has quickly gained 20k+ followers surpassing even Yuiko, while Mao chan remains under 10k. Perhaps it is her audience from her former tv announcer days, and/or her idol antics.

In the end, Mao chan will be seen as one of the most genuine casters, and will amass a fanbase who loves her dearly.