Whats a good lancer build?
Depends on what horse you want to ride, I'd recommend only going the agility you need to get riding requirement for horse of choice.
21/15 or 18/18 are my favorite 1h/polearm/shield builds at level 30. If you don't want shield (which I'd recommend having shield skill) then convert 8 skills to atts and go 24/15 or 21/18.
Arabian's kick ass, but I hate having less than 6 power strike, so I don't like 21 agility builds.