Internal geared hubs require less maintenance and can be shifted while the bike is stopped. They tend to rob a little bit of power compared to derailleur systems and have less gearing range (except the Rohloff which is too expensive to consider for this discussion). They also make the removal of the rear wheel more difficult. If you buy a better quality bike, keeping the derailleurs adjusted is pretty easy and quick and you will get a much better gear range for when you do hit those hills. Also, most bikes that come equipped with internal geared hubs are lower end cruisers or so-called commuter bikes that are quite heavy.