As a resident in Osaka, I think Osaka Castle and Sakuranomiya are the best hanami spots for people new to Osaka and want to see beautiful cherry blossoms.
There are approx. 3000 cherry trees including someiyoshino, hill cherries and satozakura. In the first week of April every year, Nishinomaru Garden is open till late (entry tickets sold till 19:30) and you can enjoy "Cherry Blossom Night Viewing" at night.
Kema Sakuranomiya Park, close by Osaka Castle Park is a riverside park. Street stalls appear when the trees come to bloom. Approx. 4800 cherry blossom trees bloom beautifully along the riverbank over a distance of about 4.2km, making it truly worthy of its name "Ohanami (blossom viewing) Road".
You don't have to be disappointed even if you miss the full bloom! There is another spot where you can enjoy the late blooming cherries!