이바요 and 야 , both are used when you are calling somebody, but, 이바요 is a bit more polite than 야. 야 is used only between friends or you can use it to someone lower than you. but actually i would use 저기요 to call somebody. 저기요 is more formal way to call somebody that you dont know.

이봐요 is like saying "Look.", it's more informal than "이보세요". I'd not say 이봐요 or 이보세요 to mean "Look." or to call a stranger. In spoken Korean, 이봐요 can also mean "Look here" or "Look at this". You can call your close friend(your age or younger than you) 야("Hey!"), it's very casual.