Siri is easier to like - she is less rule-bound and yet smart and brave. I liked her from the start, but I think I started to adore her when she basically decided 'fuck it' and blew up at God King. Also, I am now at the part where she is teaching him to read/write and I automatically go for spreading literacy. So yes, big Siri fan.

Vivenna is very dutybound and wouldn't be the life of the party but I like how quietly strong she is. In some ways, she is a lot scarier than Siri (and I get the sense that while it's still untapped, Siri can be plenty scary).