Hello everyone.
As an owner of both the JBL SRX728s and QSC KS118, I can tell you that the KS118 is in a whole other league compared to the KW181s. It is louder and goes lower while staying clean and full. I have several years of experience with all 3 of these subs. 2 of the new KS118s are easily louder than one 728s, though the 728 gets lower (to be expected, as when you go low you give up some volume due to physics), and sounds a little better. So that's still my A rig sub, and I also have 10 them so my A rig is quite scalable.
That all said, the KS118 blew me away. It gets used for EDM DJs all the time as a D rig rental and they can't believe that 1 of them obliterates a bar like it does. It has been a good money maker, as my larger A, B, and C rigs gets rented less often. Right now, the 728 is the A through C rig sub with tops/quantity of them changing depending on the rig.
As for tops, I agree with most folks on here. I don't like QSC tops. I have EV ETX-15Ps and QRX112s that I use for monitors and/or my main PA/delays depending on what the gig needs are. I also have the passive SRX835s, and they are outstanding. My next step up is some Danley SH46s.
To answer the original question, go with the KS118 for now. I get compliments at almost every gig I run from both band members, DJs, and the audience. At the end of the day, over 90% of the audience doesn't care as long as it sounds good and is tuned properly.