To me, the 545 is one of the best. It comes every 10 minutes or so during peak hours, is usually on time, has wi-fi on some buses, and actually beats driving in terms of commute length much of the time. The others would be the old 72, but now that it goes through SLU and Eastlake its a whole lot slower, and the 8 which tends to be impressively reliable.
How about worst lines? The 44 is awful. Never on time, and usually travels in packs of two or three. It was actually worse in the days of the old 43 that went all the way from downtown to Ballard through the UD and Wallingford. The 48 can also be a nightmare.
Tell me your opinions!