I too struggled with this question for some time. What led me to choosing the soft luggage was:
-lack of availability of hard cases and hardware
-appearance of bike when luggage was not on
-usage ( only really need at most once every for weeks)
After I had finally decided on the Givi combo. I was told by my dealer that the would not have all the parts in till Sept. The cost was pushing $650 just for the side cases and rack. The rack mount did seem convenient for mounting / dismounting and lock the cases, but detracted from the appearance of the bike when the cases were not in use. Two clear advantages of the hard cases are: locking and waterproof.
After all this I decided to go with
I was a little worried about the stability and security before I actually tried them out. After using them on a 500KM trip, I was convinced that they were great. To be honest, it did not even feel like I had anything strapped to the bike and kept putting my hand back there to confirm they were still strapped on while travelling at at 160 KM/hr. Putting them on and taking them off is a cinch. Just snap 4 buckles. I got the large bags and was concerned about having to relocate the rear indicator lights... this was not necessary. This size allowed me to carry:
-2 pairs of shoes
-2 pairs pants plus 1 travel nylon zip-off pants
and enough shirts shorts, socks and underwear for 6 days.
plus some tools
and this was without even fully expaning them.
Hope this helps. Either way, enjoy the ride.