Calling one better or worse is oversimplifying things, for sure. The suicide rate for Bipolar I and Bipolar II are about the same, so in that regard, they are both very serious illnesses.

I do understand how Bipolar I can seem a lot more serious, especially when it comes with psychotic features. It seems that way to me, personally, but that might just be because it's not familiar. Deep depression should be just as scary as full-blown mania, but to me, it isn't, since I know deep depression very well and have only experienced hypomania.