Depends on your budget if you’re looking at schools. I spent two years in Osaka studying at a language school. I definitely got my time and money’s worth out of it and Osaka is my favorite area. I also really like the dialect. Picked up a good bit of it from my fiance.
The school I went to is ARC Academy. They have locations all over Japan, though. Staff at the Osaka location are amazing people.
I have several friends who went to Kansai College of Business and Language. If you have two years to spend they can give a diploma that counts towards a working visa, which is neat.
You could also try to find people to teach you, but most of the time that means language exchange. You teach a little bit of English, they teach you some Japanese. I’ve never had much luck with this method but that’s not to say your experience wont be different.
Let me know if you want to know more. I could talk about my time at school in Osaka for forever.
Also, from Osaka everywhere is easy to get to. Best city.