Navigate your world with Google Maps, now available for iPhone. Get comprehensive, accurate and easy-to-use maps with built-in Google local search, voice guided turn-by-turn navigation, public transit directions, Street View and more. Use Google Maps to discover great places to eat, drink, shop and play, with ratings and reviews from people you trust. Sign in to save your favorite places and quickly access all your past searches and directions from your computer, right on your phone.
I’ve never really had any problems with Apple Maps (though the lack of public transport information is a pretty big failing) but Google Maps on an iPhone 4 is woeful, it stutters and lags when dragging the map around. Apple Maps is fluid and a lot more responsive. I’d hate to see how this performs on a 3GS.