From my experience I would find it difficult to say
everyone anyone 'prefers' mobi....from a format capability standpoint ePubs are MUCH more capable/prevalent. However, there are people out there with really old devices, who, for whatever reason, haven't upgraded their devices to ones capable of reading an ePub. THOSE individuals would be stuck with a mobi format simply because they don't have a choice...
...although, when it comes down to it, there are plenty of free apps that can go on your phone or tablet that will read an ePub... so it's only those die-hard eink device types that are holding back the progress of the epublishing world!
