Best transportation from Tokyo to Osaka?

I am travelling to Tokyo in October, after 6 nights we are booked into Osaka. I know bullet train or an internal flight is quickest from Tokyo to Osaka.. which do you recommend and how easy is it to get a ticket for these. Can I leave it till Ifm in Japan to do this or best to book in advance/how much advance.

Many thanks!

Flight is cheapest.
Train is faster (counting to/from airport, checkin etc) , better for the environment, less tiring but more expansive.
Ifd get the train, Japanese train journeys are a joy.

Train is way faster, and probably cheaper unless you can get a heavily discounted fare. Bus is slow, not that much cheaper.

Shinkansen tickets you can buy until a few minutes before departure and have practically fixed prices not like flights. Definitely train is the most comfortable.

Flight ..
get to airport, check-in, wait for boarding, wait for plane to fly, wait/sit doing nothing in cramp sit, waiting to get-off plane, wait for baggage, transport from airport to destination

shinkasen
maybe 1/3 of the above

bus
overnight bus save time, cheaper.

I would go for the shinkansen with no hesitation. It costs approximately 15000 yen one way, vs. 11000 yen for flights (using special fares for foreigners). So it is a bit more expensive, but you don't have to go to the airports (which costs money and time). In addition the travel time is not that different if you include all waiting time at the airport and such. Finally, it is more comfortable for sure.

Actually, traveling on domestic flights are way much easier than on international flights. But unless you're coming from and going to a place very close to the airports, or unless you want to use your airline miles to the fullest, most locals including airport freaks like me would travel on the Shinkansen. You'd be guaranteed a great view of the Pacific ocean, and you can enjoy your chances of seeing either a big figure of Mt. Fuji or no figure at all. The "eki-ben" train station lunch boxes are a treat too, especially because the airport "sora-ben" are no-longer available.