Personally, I would argue that military successes get too much of the press. For military successes to have a chance of establishing a "Germany" (rather than just be an imposed alliance), they had to fall on fertile soil--namely, feelings of "Germanness."
Railroads and industrialization more generally were each indeed crucial--but don't think of industrialization solely in terms of heavy industry (iron and coal). It was also about interconnectedness--including feelings of interconnectedness. For instance, Die Gartenlaube (translates as "the Garden Arbor") was a weekly illustrated magazine started in Leipzig (Saxony) in 1851, using new printing technologies (and cheaper paper). A sort of highbrow educational magazine, it could be distributed easily and widely, in part because of the growing transportation infrastructure (railroads, roads). It became hugely popular throughout all of the German states... north to south, Rhine to Prussia.... everywhere there were German speakers. As its circulation expanded, it became THE magazine to be read by educated German-speakers... and as such, its editors increasingly included articles from all over the different German lands. It thus offered stories and illustrations of a de-facto "Germany" before there was one, i.e. articles on life-saving boats in north German coast, next to articles about the Romantic landscape of the Rhine. "Germans" got used to reading about and even seeing different "parts" of this (linguistic and economically-tied) region as parts of a whole, because it was all contained in the pages of a single magazine. It was a Germany-wide magazine before there was a "Germany." It's circulation was just shy of 400,000 copies in 1870, but multiple millions read it (with borrowed copies, etc.). And its educated readers included not just lawyers and businessmen, but the ranks of the various state bureaucracies, from Prussia to Württemberg. When war with France came in 1870, Germans were used to thinking about "German" lands as interconnected... and France posed a definite threat to this "Germany."

Germany was not just imagined but seen in print before it came into being through diplomacy and military means.

(see Kirsten Belgum's great book, Popularizing the Nation: Audience, Representation, and the Production of Identity in Die Gartenlaube, 1853-1900)

EDIT: grammar

Determining "more important" is entirely impossible in this situation; all the components were necessary acting together to allow German unification to happen when it did. History is very chaotic and, ultimately, unpredictable. Any small detail could have changed everything completely out of the realm of Bismark or Industrialization. I know I'm dodging the question but that's very intentional; these types of questions serve no purpose in my opinion as they were both vital components.

I've written extensively on the conditions of German unification; I'd look at these posts first and foremost for any concerns about it.

• Why did "Little Germany" (Bavaria et. al) unify with Prussia?

• Why did it take so long for the German Empire to form?

Coincidentally the first one speaks more about Bismark's influence on the formation of Germany and the second has to do with, well, all the other reasons. So a combination of these two posts should give you a pretty clear idea of unification and, from that, you can make your own personal conclusions of which you think were more important :)