I prefer the STL in Card's Ender's Game series. They asymptotically approach the speed of light so the passengers only have several weeks pass when travelling to far flung locations but the universe around them experiences a normal passage of time which may be tens of years. This has really big implications on the plots in several stories.
They do have an ansible communications system that does allow instantaneous communication over astronomical distances.
Do you have to ride a world sized turtle to traverse it?