Famitsu Magazine's January 2021 issue had released the results of its Genshin Impact Fan Survey that they run on their 3 platforms: Famitsu website, Famitsu mobile app, and Dengeki Online. The survey ran between Nov. 6 to Nov. 15, 2020. There were (less or more than) 1850 people who responded to the survey.
Survey Demographics: 82% Male, 18% Female. Most responses are in their 20's, followed by 30's and 10's.
Take note that this survey is mostly influenced before the Patch 1.1 update.
Original article here: 『原神』ユーザー1850人が回答したファンアンケートの結果を公開！ 好きなキャラクターやいちばん苦戦した魔物は？ - ファミ通.com (famitsu.com)
Note: Take note that I use machine translations here, so these translations are kinda bumpy. Feel free to comment if you spot any mistakes or correct some translations.
There are some who liked them because of their cuteness or coolness, but more than that, they like them because of their strength and utility. There are also people who like them because of their mobile Elemental Skills, which can be useful for exploration.
10.) Jean (85 responses)
9.) Barbara (89 responses)
8.) Noelle (101 responses)
7.) Fischl (107 responses)
6.) Mona (121 responses)
5.) Lumine/Hotaru/Traveler (Female) (131 responses)
4.) Qiqi/Nana (139 responses)
3.) Diluc (156 responses)
FBI bait Jean bait Klee (207 responses)