This would be close.
I think Kaine is a slightly superior politician. He has won statewide office three times, winning the bigger races by better margins than Kasich in Ohio in 2010. Republicans need to win Ohio, while Democrats can afford to lose Virginia.
Kaine's weakness is that Democrats have held the White House for the last two terms. As a Senator/ former DNC chair, he can't exactly run as an outsider.
I'd give Kasich the edge due to the tendency of parties to do worse in the third term.
Kasich/ Martinez- 282 Electoral Votes
Kaine/ Klobuchar- 256 Electoral Votes
Explain to me how does Kaine lose Pennsylvania I'd argue he's a much better fit for PA than Obama ever was I'd think he improves among whites there and Eastern PA.
Kaine's in a worse position than Obama was. He's a candidate who lacks the advantage of incumbency running to get his party another term in the White House.
I'd also imagine decreased African American turnout without Obama on the ballot. In 2012, African Americans were 13% of the voters (slightly higher than their share of the population) and 93% went for Obama.
Kasich would also have an advantage in Pennsylvania coming from a neighboring state. Even if Kaine's a better fit for PA than Obama, Kasich's a better fit for the state than Romney, McCain or George W Bush.
Neighboring state?
In 2008 Barack Obama of course won Illinois by an overwhelming majority, Iowa and Wisconsin by decisive majorities, barely won Indiana, barely lost Missouri, and lost Kentucky by a huge margin. Arkansas and Tennessee come close to Illinois on their extremes, and Obama lost both handily. Technically, Michigan has a water boundary with Illinois, and Obama won it by a margin in the high teens.
John McCain won Arizona decisively, won Utah by a huge margin, but lost Colorado (at a point) decisively and lost California, Nevada, and New Mexico by huge margins.
Bill Clinton never won Mississippi, Oklahoma, or Texas. He should have been a good cultural match for Texas.