Qick results, with good schedules & prices.

Better than other sites for results.
Didn't give me a slew of insane schedules like 12+ hours overnight(!) layovers (transatlantic return). Those are an insult, generated to show initial low prices, but utterly unacceptable for normal people. (Bait and switch tactic).
Easy navigation, straightforward booking.

Didn't have to erase cookies to give me the same price the second time; other search engines leave a cookie (or cookies) behind, and when you search for the same route for the same date, it gives a higher(!) price on the same route, time and carrier. When I delete(d) the cookies, got the same (lower) price again as the first time. So it's proven (to me) tactic. Smartfares didn't do this travesty.

This is a really sore point with me. Several other fare-search engines I do not use anymore b/c of this underhanded tactic to scare me into a purchase at the now higher price - fearing an even higher price the at third time search.