I suppose it depends - as ever - on how far you'll be going and what the conditions you're likely to encounter will be like. Disk brakes are (so I've heard) a whole bunch better in the wet than rim brakes, not least for braking performance but also for pad wear and rim wear.
I commute ~ 7 miles each way on an entry level MTB, with rim brakes. I've been doing it since Feb 2008 and have barely missed a day since then. During last winter (when it was wet), I was having to replace brake blocks every 5-6 weeks. Since March this year, when we've not had much rain darn sarf, I replaced one set in July and then just had to do another set a few weeks ago. It's got quite wet again darn 'ere in the last few weeks and so my new-ish blocks are already showing significant wear.
I also had to replace both the front and back wheel during the course of last winter, purely due to rim wear. This despite being fairly pernickety about keeping the rims clean, replacing blocks and so on.
My commute home takes me through a few hundred yards of woods with deep muddy puddles. As a consequence, I pick up mud and grit on my wheel rims. I then have about a mile of downhill on a single lane country road, which means I'm braking rather a lot. You can hear all that freshly picked up paste grinding away brakes and rims as you go.
I looked at replacing my commuter with a Giant Escape M8 (hub gears and brakes - I'll let someone else explain how they work!!) for lower maintenance this winter, but work have just arranged to relocate a whole bunch closer to (my) home so my commute will be ~3 miles, nearly all in the woods. Given that, and as the Escape has been discontinued, I'm wondering whether to just get a better MTB with disk brakes ..
