If you are already a fan of Kamen Rider, then Nexus would be a good choice. It is far from a traditional Ultraman series, but it has some elements that can be quite positive for a newcomer.
1. The show is basically "Kamen Rider in a Ultraman costume". It moves beyond the monster-theme and focus a lot on drama and the mysteries that lies within the powers of the Ultramen. In many ways, the theme of this show reminds me a lot of Agito. So if you enjoyed Agito, you will definitely enjoy Nexus.
The idea is, that you get to experience a little bit of the Ultraman universe, while staying with some of the more familiar elements from the other Toku shows that you already enjoy. It makes it much easier to enjoy and it gets you ready to fully enter the new universe.
2. When you have been watching KR and SS, you have gotten very used to team-fighting or multiple heroes in one show. While most Ultraman shows did have some team-up battles, it is mainly a one-man show with only 1 hero. But in Nexus, you have two Ultraman almost from the start, who are FAR from being buddies. This leads to a lot of great fight scenes. Other Ultra series have tried introducing an "Evil Ultraman" character. But it has never been more than a monster-of-the-week thing.
Ultraman Gaia introduced the idea of rivalry between two Ultramen, but Nexus took the step even further and made an evil Ultraman, who is a recurring character of the show, and most Nexus fans will agree with me when I say that he is insanely awsome! :thumbs:
3. Nexus can be found fully subbed. It is very hard to find subbed Ultra shows sadly. Nexus has been fully subbed, Mebius has been fully subbed, Tiga has been fully subbed and Ultraseven-X has been fully subbed.
Other than those, most other shows have only been subbed halfway through or has not been subbed at all! I am not sure if the original Ultraman was subbed as well. I just know that it was dubbed.
Many people talk about Max, but as much as I love Max, I would never recommend it to a person who has not seen Ultraman before, for the sole reason that it is very hard to get into if you are not a big fan of the monster theme to begin with.
I would rather take Nexus first, then move on to Mebius. By watching Mebius, you basically get a whole lot of background story of all the old Ultramen, their enemies, their allies etc. The old actors even return during the last part of the show.
Mebius is not a perfect Ultraman show, but it is still easy to get hooked by, while Max is a little bit harder unless you really love monsters.