姉 is more common in Japanese. Generally, as a family member, older sister is called 姉（あね）. Mostly younger brothers and sisters call her 「姉さん（ねえさん）」, when they’re grownup. But some men use 「姉貴（あねき）」, or some women and kids use 「お姉ちゃん（おねえちゃん）」. Outside persons use “ your/his/her/their お姉さん” It’s not only for real family, we call a close older friend 「お姉さん」. For example, I have an older friend whose name is Yuki. I can call her 「ゆき姉（ゆきねえ）」.It's a kind of honorific title. Whether we truly respect the person or not, Japanese people like to put a title after the name. Often call just the title. You know "Sempai", "Chief", "○○'s Dad". In our customs, we're afraid of calling the direct name of the elder person. Also we use it for unknown women friendly. If you find a woman who looks something trouble on a street, “Hi, お姉さん. Is everything ok? Can I help you?” For a waitress in a casual restaurant or bar, ”Scuse me お姉さん! Order please!” Like that. On the other hand, 姐（あね）reminds us a wife of Yakuza’s boss. Yakuza is Japanese traditional gangstars. They organize into family groups. The members like henchmen call the boss’ wife 「姐御（あねご）」or「姐さん（either あねさん or ねえさん）」. She can act on the boss’ behalf. Almost all Japanese people know that through movies or comics about them. So we sometimes use 「姐御」as a nickname or jokingly. If a young man/woman was helped a job by his/her older co-worker woman, he/she might say “Thank you very much, Anego!” Nowadays 姐御 and 姉御 can be seen. Some strict writers pay attention the kanji, but not so many. For normal Japanese people, Anego（姐御/姉御） means a woman who is dependable, reliable and good taking care of younger people. That’s why, 姉 has broad utility. Conversely, 姐 is a little bit old-fashion and including specific impression. oh, I didn't notice you chose the best answer already. I'm happy if this would be the supplement.

姐 is a variant of 姉（both read as あね）, but you will most likely see 姉. I, personally, have never seen the 姐 written in modern Japanese writing. 姐, however, is standard in modern Chinese. :)