My first choice, SPG, second, HH, third, HI.

(1) SPG is the best program going, but in some markets they are poorly represented (if at all) and in others (primarily Europe) are typically too expensive.

(2) Hilton - a decent selection of properties, and decent treatment as a mid-tier elite.

(3) Holiday Inn - if (1) and (2) aren't available or too expensive, at least I can earn a few points. After 3 years, I have enough for a free night in Europe.