I booked the Accor ibis Styles Osaka Namba. Haven't stayed there yet, but right next to Dotonbori and reviews were good. Fairly newish hotel I believe. The Dotonbori hotel (one with all the big heads in front of it) seems like a popular option as well. I've stayed at the Sheraton Miyako Hotel Osaka, which is right above the Uehonmachi station and one stop from the Osaka Namba station. Location was great as you don't leave the hotel to get to the subway, but the hotel itself was kinda meh.