I'm 5'8" 30 inseam riding 19.5 at the moment. Shorter legs.... I go with the larger frame for the longer reach... longer torso.
Years ago I wanted to buy a Rockhopper, 26 in. wheels. I wanted the 19 in.. they didn't have it and the sales person talked me into the 17 in. frame. I hated it. Too small.
Never listen to people and websites about which size to get..(me included).. go try the bike to see if it fits.