I use Tusk Pilots with bottle holders and like them a lot. They're tough, durable, 35L each. The shell is more water resistant than you might think (virtually waterproof) and they have included dry bags. I have redone the straps that normally go over the seat to just wrap around grab bars, etc. My wife appreciates not having to sit on straps and buckles.
For a few extra bucks, I'd go with the Tusk Olympias next time with the quick mounts. They're a bit higher capacity, with larger bottle holders included and of course they're removable in 10 seconds, rather than 10 minutes.