This is sort of the opposite of this question: Which SciFi universe has the fastest space ships (hyperspace technology)?
Since the obvious answer is just wherever there is no technology much more advanced than our own, we need to modify the question.
In order to force a unique answer, the metric we will use is: In which universe, despite having slow drive technology, have people traveled the farthest and spread over the most worlds using non-FTL drive ? The non-FTL drive has to be used because it is the fastest drive available, not for some quirky exceptional case. I.e. no one has FTL.
Obviously teleport-type technologies etc. are not allowed. There is no cheating.