The ways to say hello depend on the country, for example: In Spain: “Hola, ¿Qué tal?. In Mexico: “¿Qué onda?”. In Cuba:¿Qué volá?”. In Chile: “¿Cómo estay?”. In Panama: “¿Qué xopa?” In Puerto Rico: “¿Qué hay?”. In Colombia: “¿Qué hubo, mijo?” In Republica Dominicana “¿Qué lo qué?” In Venezuela: "Alo" or "Epa". That's all I've heard. These greatings just are variations, of course they mean the same.

Hola is the best one because it works for all the situations, but you can also say "¿qué tal?"/ "¿qué hay?" / "¿Qué pasa?" / "Buenas" (when talking with friends or family) o "buenos días/buenas tardes/buenas noches" (in more formal contexts with people you should show respect to). (I'm talking about the Spanish from Spain, in some other countries some of these possibilities might not be valid)

Besides "hello", people mostly greet each other with "good morning" "good afternoon" and "good evening". Good morning = Buenos días Good afternoon = Buenas tardes Good evening = Buenas noches Sometimes "Buenas tardes/noches" is shortened and they will simply say "Buenas".

Well I'm not a native or fluent Spanish speaker, obviously, but, in Argentina I think they say or said "che" as a greeting. "Oye como vas" (look, how's it going) might be from Puerto Rico or something. It's the title of a Tito Puente song, covered by Santana. Check my facts with a native speaker but I think I'm right.