>>26548294watch adventure since its the original but also is generally seen as the best season. skip out on 02 unless you really loved adventure. watch tamers. theres nothing else that can be said other than watch it. its that good.
frontier is meh, but the designs were good so there is that. savers is really fun, has a different style from the norm and is really enjoyable. xros is my personal favorite. its super mecha inspired, has a lot of great animation and fun times. skip young hunters unless you really enjoyed xros.
tl;dr adventure, tamers and xros are top tier