Subways and trains are the best way to get around Osaka. A prepaid Icoca card is the BEST way to pay for transport (but a Suica or Pasmo card from Tokyo will also work just fine). Taxis are excellent but expensive. Buses are not recommended for short-term visitors.
Getting Around Osaka Osaka covers a huge area, but it is all connected by a superb public transport system.
Here is how to get around the city:
Osaka is huge but it is very easy to get around using the city’s excellent public transport system. 5 of the city’s main hubs are conveniently located on the Midosuji subway line, that runs north to south right through the heart of the city.
From north to south, here they are: Shin-Osaka, Kita, Central Osaka (Honmachi), Minami, and Tennoji.
There are only two main tourist centers: the Osaka Castle Area and the Osaka Bay Area, that are off the Midosuji subway line.
The Osaka Castle Area is easy to reach from Kita by the JR Osaka Loop Line, or from Honmachi via the Chuo subway line.
The Osaka Bay Area is also reached by the Chuo Line or the JR Yumesaki Line.
You can ride the JR Osaka Loop Line with a Japan Rail Pass, but if you just want to explore Osaka for the first few days after arriving in Japan, it is best to activate your pass on the morning you leave Osaka and use it for your long-distance train travel (ie, use the pass to pay for expensive intercity travel, not for cheap local travel).
A prepaid Icoca card is easily the best way to pay for train and subway travel in Osaka. If you are coming from Tokyo, your prepaid Suica or Pasmo card will also work just fine.