The Cortech tribag system is awesome. The saddles are on and off in 3 minutes. You can put the saddles on with the straps under the seat if you want. The tail bag can clip to the saddles, bungie (it has BOTH!) or both for added security.
I'm 200+ miles from home this weekend. My wife and I traveled on the bikes for the weekend. I had the tribag system on plus before mounting the tailbag, I put a backpack on top of it with the should straps cinched around the tailbag, then mounted the tailbag, thus making a 4 bag system. I'll have to get some shots of it tomorrow morning before we journey back home. She carried a backpack with her with some lighter stuff.
Search is your friend because I've seen a thread with these questions and I know I put a few shots of my tribag system in there.
The choices are MANY and it all comes down to preference. Good luck!