I purchased MEC panniers for a tour this year. I had looked at Ortieb, Arkel and a few others. For $$ you can't go wrong with MEC. My suggestion would be you make or purchase raincovers or do what I did - line the pannier with a plastic bag.

http://www.mec.ca/Products/product_d...=1168402554697

I found them very durable ( I beat the crap out of my gear ), at first glance, more durable than Ortlieb and other more expensive brands. I get the impression that the Ortliebs ( or MEC Aquanots) may rip or tear if snagged on branch etc.. My buddy has had his for about 6 years, through Mexico, the US and Canada, never any issues. I would stay away from the Vaude brand they carry..seemed rather flimsy and may be prone to breakage.