I've had/have all of the aformentioned. Toured the AxeFX for 10 years, the Kemper for 7 and had most of the line6 stuff since the orignal pod. I've used them all extensively, professionally live and in many released recordings. I can give you a short answer to this in 2021..
They can all sound like each other these days but you just won't have the time to truly learn them all in greater depth. So go with the one that has the most intuitive interface/software/hardware for you, then start peeling back layers. They all have presets that mostly suck and that is no way to judge any of them. Of the three Line 6 offers incredible value, reliable intuitive software and tons of history knowledge in modelling. Do your research, go with what you feel will work for you and your budget best and just get your hands dirty!
As a guitarist there is no greater time to be alive! (well... except maybe the 80s, but most of those guys and girls cant hear anything anymore lol)