Based on my experience, I would go with the knife blade. It won't be brilliant, but it's a backup, and you can use it for 'crud' work like stripping cable or scraping parts.

I find the standard Leatherman file to be essentially useless on hardened steel (axes, knives). It will work reasonably well on soft steel like shovels. Do not expect it to match the performance of a real file from a hardware store. Not even close.

The only Leatherman file worth having is the diamond file. These are in the Wave and Charge (all versions), Surge, and two retired models (PST II and Pulse). Highly, highly recommended. It's a primary reason why I carry a Wave II.