I'm partial to *standard* panel loading cordura bags with rain covers...Robert Beckman World Tour...similar to the Lone Peak offerings. Loading and sorting thru gear just seems simpler and more efficient, and I've never complained about sliding on the rain covers when needed. To be fair, I haven't toured with the roll-top bags but the design appears a bit clumsy.
...for the Ortlieb users...
Waterproofing is a two way street, correct? How does one keep the inside of the bags "fresh" on a long tour? Is mildew a problem?