I don't think there was one consistent team over the past 15 years.
The Roosters did well until 2005 and that's when inconsistency and making the finals every second year came in. Ironically when Fittler retired this inconsistency came in.
Broncos were similar but up until 2009, again the retirement of Lockyer coincided with their drop in overall form.
Manly have been almost the opposite, they were doing alright in the late 90's, merged with Norths, became terrible, un-merged (if that is a word?), rebuilt and began their run of finals since 2004, when Des Hasler started coaching the team.
Similarly, Melbourne were decent in the 90's (1999 again they had a plethora of players from the defunct clubs from the defunct Super League), again began their run with the coaching from Craig Bellamy. Sure, they did cheat of course, however they still tasted success in 2012 with their first legitimate premiership since 1999.
I'd have to go with Brisbane as they have the most NRL premierships (3) as well as making the finals every year up until the 2010 season.