I've been researching the same thing and come to the conclusion that there isn't a single system(without mods) that will cope well with all situations - on road/off road, short trips/long trips, one up or two, close to civilisation and gas or not, security when away from the bike etc.
As my first trip is going to be in europe and largely on road, I've opted to start my foray into the world of motorcycle luggage with a set of KTM black aluminium cases (rebranded SW Motech Trax Evo) on their quicklock rack system. Adaptors are also available for Hepco and Becker, Givi, Shad, Kappa Monokey, Krauser K3, 5 and 7. The cases are lockable to the bike as are the racks themselves. They already have securing loops on the lid for taking either a set of carry handles or a wide range of other waterproof bags including the Kriega US's, the Wolfmann Rolies and the Trax Evo expansion bags... or anything else you care to strap on there with some webbing.
The added advantage of this system is that the whole rack can be removed from the bike in a few minutes, leaving only the inconspicuous mounting bolts and clearing the way possibly for a Giant Loop Great Basin for those one up trips with a more off road bias where less storage is required and security is less of an issue. Or I can go another route and get the Wolfmann Expedition saddle bags, for which there are now specific soft luggage adapter plates available here in the UK:
They are mountable on the quicklock system and with the appropriate bases will also allow me to carry up to 1.75 gallon rotopaxes, secured on the rack beneath the bags.
That's where I've got to.....
Expensive business this adventure biking!