Too many good choices. The most important to me would be having a highland games to go to and enough notice that I could get the time off. The easiest for me would be Denver for those reasons. I live close and always have the time for the games up in Estes Park. Now, as far as the other cities go...

Chicago, Illinois - born there, don't want to go back
Atlanta, Georgia - realitivly close to the Grandfather Mountain games...
Toronto, Ontario - Grant would be the co-ordinator
Houston, Texas - Zardoz would be the co-ordinator but it can be VERY humid
Vancouver, BC - Not that easy for me to get to but like what I see of the area
San Francisco, California - well, ok. Nothing against it but nothing that pops either
Denver, Colorado - said above
Washington, DC - Too many other things I'd want to do while I was there
Boston, Massachusetts - Barb would be there.
Fort Lauderdale, Florida - humidity, are there any games?