For me my favorite characters pretty much always stays the same like with Hanna in PLL or Elena in The Vampire Diaries and even Clary in Shadowhunters they were my favorite characters from the first season and it hasn't changed even to now..it's very rare for me to actually change my favorite character to any show.

It does depends on the show, but rarely ever. Usually it's only if a new character is introduced that I fall in love with even moreso than the other (- ie. Cas took place of Dean, in Supernatural.) or there was serious character development (ie. Bellamy took place of Lincoln in The 100).

In the beginning it might change a little but by like episode 10 or so I've usually found a favorite and I stick with them.

I changed my favourite characters from shows that I started watching when I was really young for example Haley used to be my fave from OTH but now it's Brooke <3 And Naomi used to be my fave from Skins but now it's def Effy <33
Can't think of any others tho

Depends on the show and the season, but usually I don't.

Usually my gut feelings are 100% correct and I love my favorites for the course of the show.

Almost never, I always have a really good feeling about who I love the most and for the most part it doesn't change even if they do something I don't like.

I agree with MTahmisian that it depends on the show and the season.
My favorites in Teen Wolf and Shadowhunters have always been Derek and Magnus, but it depends on the season for The 100. For seasons 1-3, my favorites are Lincoln and Octavia, but in season 4 they're Bellamy and Raven.
But sometimes my favorite character changes when I rewatch a show (The Vampire Diaries, Merlin, Buffy)