You mentioned island-hopping, so this probably wouldn't be an issue for you, but my HI trips are to Kauai, which has no Hilton properties AFAIK. So Hilton cards aren't useful to me for that. There are some nice SPG and Hyatt properties there, though. Spouse and I will probably both get Hyatt cards prior to our next trip so we get 4 free nights at their resort on Kauai.

Always pays to check your possible destinations and see what chains have availability where you want to go, and keep it in mind when deciding what cards to get.