For primarily cutting metal bar stock the rigidity of a milling machine is hard to beat. Aluminium sheet goods different story if that's the goal.
With a 26" depth restriction a C frame mill wouldn't have much Y travel so that's one of the reasons a router may have more appeal.
Some of the heavy duty DIY router builds showing up here look a lot like bridge mills, the closer your router resembles one those builds the happier it will be cutting metal.
Of course what's possible in a build will depend on your access to tools, some of the posters here have workshops that resemble mini-factories.