I always hand-build them. Sometimes in random quick MP games, I would purchase one, thanks to tradition and monarchy. Liberty for me is never a smart option unless there is plenty of space to expand around my capitol and by that I mean something like 5-6 viable good spots, involving at least 1 LR, preferably a different kind each time just in case. Why grab liberty opener and republic, +1 culture and +1 production to get a free settler when you can get tradition? It covers border expansion, culture, defence, growth, gold and wonder production all into one, and with the additional citizens, you effectively eclipse the liberty settler production bonus. The liberty tree needs a stronger happiness buff and a gold buff to be more attractive in BNW.
I have also tried 2 games on immortal level doing a liberty start and I fail to see the benefits. The civs chosen were Carthage and the Netherlands.