Do you book your trains to other cities online or at the train station?

Hi All – I am heading to Japan next month and was looking to book train tickets for the 4 of us. We won't be using the JR Pass as i used the calculator and it turns out that one way train tickets are cheaper. We need them for Tokyo – Kyoto, Kyoto – Osaka, Osaka – Hiroshima. A friend suggested that i buy once I get to the station but i don't know whether it's a good idea.

Hoping to get tips on how others book these? Thank you

by striker797