Which route is fastest? And which should I learn for a first time run?

For which story? For sonic's story, you should learn Linear Route for a first time run. TAS Route is faster but not by much at all and the movement is very hard to optimize so it would end up being slower for a beginner. Glitched Route is slower by around 30 seconds so don't learn that one. If you're talking about a different story somebody else can help you out.