Charapedia asked 10,000 anime fans the question: Which supporting female characters would you like to see as the protagonist? And from thousands of fans, most of the responses are from the female fans (54.1%), male fans (45.9%) and teens to their 20s (79.3%) while the other 20.7% are 30 and over.
Fans also voted for male support characters which can be seen here.
Here are the results:
20) Tomoyo Daidouji (Cardcaptor Sakura)
19) Erza Scarlett (Fairy Tail)
18) Mikuru Asahina (The Melancholy of Haruhi Suzumiya)
17) Sayaka Miki (Mahou Shoujo Madoka Magica)
16) Touka Kirishima (Tokyo Ghoul)
15) Suzuha Kirigaya / Leafa (Sword Art Online)
14) Nico Yazawa (Love Live! School Idol Project)
13) Chino Kafuu (Gochuumon wa Usagi Desu ka?)
12) Yukiho Kousaka (Love Live! School Idol Project)
11) Azusa Nakano (K-ON!)