Given the leaked version of Trump's speech tonight, he's attacking Clinton for being establishment. Doesn't she need someone who's perceived as anti-establishment, or at least a little colorful, like Franken? Literally the only good things I've heard about him are that he speaks Spanish and he's a member of the Foreign Relations Committee. Even Bernie would be a better pick than Kaine.
Making a running mate selection based on a knee-jerk reaction to Donald Trump's attacks is foolish and not something I think Clinton would do. She needs to consider who would best help her govern as President, with a secondary eye toward electoral concerns.
Others have stated that Clinton is most concerned with someone who is most ready to step in as president if something should happen to her. Kaine is a U.S. Senator (statewide federal experience) and former governor (statewide executive experience) of a major swing state. He's also a former mayor (municipal-level executive experience) and DNC chair (Democratic party connections). He sits on both the Senate Armed Services and Foreign Relations Committees in the Senate (foreign policy credentials). He's also a former lieutenant governor, so he even has experience being a No. 2.
Also, it appears Kaine is the choice of Democratic Party insiders. Clinton is part and parcel of the Democratic Establishment, I think she is likely to go with the party consensus.
http://www.politico.com/story/2016/07/tim-kaine-hillary-clinton-vp-insiders-225634 
