I've only played South Seas but I've read the rules of New World. As jungleboy noted, New World requires more foresight and strategy. I believe the only core-idea difference between New World and the standard game is the removal of meeples in unfinished features east of the surveyors (correct me, please, if I missed more important things by just reading the rules). I imagine it's a very unpleasant moment to have a meeple removed from a monster city-to-close. Your opponent(s) may strategically score small cities and short road frequently and expedite the movement of the surveyors.
South Seas offers a peace of mind in terms of removing meeples. You can voluntarily retrieve a meeple without scoring, anytime, given that you don't place a meeple in that turn. It's like 10 year festival all the time! Much of your attention can then be devoted to deciding whether you want to harvest more shells or bananas (in some cases fishes) if you want to load that 6-point ship.
Special thanks to Hounk, to me who introduced Yucata.de and South Seas thereby.