The question of what a digital comic book is worth–and whether its value to a reader is correlated with the value of the same thing in print–is wide open right now.

While a comic like "Action Comics No. 1" can sell for millions, this is the exception. Still, here's the criteria a valuable comic will need to meet.

There are comic books currently worth in excess of £3 million, some have appreciated in value by 344% in under a decade. I take a look at the top investments right now, some of which are beating ...