It used to be that ASIS was considered the "end-users" show, while ISC West was considered the "dealers" show. ASIS used to show the high-ticket items (such as armored vehicles) and guard and investigative services, while ISC had the "parts and pieces" (contact switches, wire, tools, etc.) that were of more interest to installers. Over the years, ISC has become a little more like ASIS and started targeting end-users, while ASIS appears to have shrunk and doesn't have the allure that it once did (at least IMO).
I usually always go to ISC West, and ASIS every other year unless I have a client who asks me to go along with them. I feel that ASIS has the best educational seminars, and if you are a CPP or PSP, attending the seminars at ASIS is the quickest way earn lots of CEU points.
Everybody has a different opinion on cities; Las Vegas and Anaheim are convenient for me, while the mid-west and east coast locations are less attractive. I'm sure people located in other areas feel the opposite.
It's expensive to attend these shows when you factor in airfare, hotels, rental car, etc. If you work for yourself, attending also means the loss of billable time, the cost of which can exceed that of your direct expenses. I figure that it costs me in excess of $5,000 for every show I attend.
I almost always gain something from attending, but am not sure that it is worth the cost. There are so many other ways to learn, gather information, and network these days that I am starting to feel that the trade show is a dying institution.