Exploring Shikoku by rental car or train?

Hi
I plan on visiting Japan and Shikoku in early April next year. Spending about 5-7 days. I do not plan on visiting Naruto or Tokushima but places like Kochi, Takamatsu, Uwajima, etc. I also like to do the Shimado Kaido cycling route. So maybe start in Onomichi cycling to Imabari and then rent the car there going around and returning it and oneard to Osaka by train.

Since there are areas hard to reach by bus and train car would be perfect,but not sure how it would be best, to rent a car at different places and do local exploring and doing the long travel by train or simply rent one car.

Not sure about the roads so hard to plan acvordingly...

Kochi, Uwajima and Takamatsu are all accessible by public transport so I really wouldn't worry about it. If you were going to somewhere like Iya Valley a car would be a very good idea.

I spent 10 days travelling in Shikoku a few years ago, and managed nicely without renting a car. I did use taxis a few times but mostly trains and buses. If you are planning to visit some remote areas where public transport is not available, renting a car would be a better option.

I would recommend Shimanami Kaido.
just last year, I rent a car from Onomichi (Hiroshima) and toured some islands between Shikoku and Hiroshima. Just splendid!