I used to play with my ring finger when I first started playing but then when I started trying to play more brutal death metal stuff I found it extremely difficult.
On songs where there are a shit-ton of power chords played pretty fast for several bars, using your ring finger becomes very uncomfortable.
And using the pinky comes into it's own,
I suppose it's because for most people it's less of a stretch, and because those riffs are mainly comprised of power chords, you just need to keep the same shape.
Like on this; (part 8)
http://riversofgore.com/Tabs/yura/Suffocation/InfectingTheCrypts.htm
Obviously if you add the octave, then you just use ring and pinky, using the pinky to bar both strings would be nuts.
But when you can use both fingers with equal comfort, then there really isn't an issue, you can use both whenever they are needed.
And swapping the between them takes no effort, in fact I do this fairly frequently without even noticing.
I'd say learn to use both.
and +1 to Torniojaws