I don't know that I'm qualified to really answer this, because I didn't start reading American comics again really until last year. Took about a 10 year break for the most part. I'd like to do this again in a few months, when I'm sure I will have a different perspective after getting through some stuff I'm really looking forward to reading.
Favourite Ongoing
Western: Birthright, Giant Days, East of West, Deadly Class, Pretty Deadly, Southern Bastards, Saga (less so lately)
Japanese: Berserk, Otoyomegatari, Vinland Saga, Hunter X Hunter, One Piece (until the time skip)
Favourite Completed Runs
Western: Scott Pilgrim, Essex County, Watchmen, first couple trades of Geoff Johns' Teen Titans (but this is nostalgia. I haven't read it in 10 or 12 years), New 52 Batman, Astonishing X-Men or... some arc I don't remember from when I was a child.
Japanese: Itou Junji Kyoufu Manga Collection, Solanin, GTO, Eyeshield 21, Shonan Junai Gumi, Sanctuary, Homonculus, Kindaichi Shounen no Jikenbo (Case Files)
Favourite Artists
Western: (I'm not too familiar with the names) Jock, Emma Rios, Fiona Staples
Japanese: Miura Kentarou, Inoue Takahiko, Murata Yuusuke, Hirohiko Araki
Favourite Writers
Western: Warren Ellis, Jonathan Hickman, Frank Miller, John Allison, Brian Lee O'Malley
Japanese: Itou Junji, Miura Kentarou, Hirokane Kenshi, Kago Shintarou, Matsumoto Taiyou
First Comic?
Western: First one I read was probably a random Spider-Man or X-Men one. First one I really got into was either Uncanny Xmen or Teen Titans.
Japanese: Kindaichi and Doraemon were given to me as a child from a Japanese exchange student. That's when I first discovered manga.
Favorite Character?
Western: Gambit when I was a kid... Maybe Esther from Giant Days or Batman? No clue on this one. I did always love Spider-Man...
Japanese: Onizuka Eikichi was when I was younger... Maybe Thorfinn or Guts now?
Favorite Scene?
I don't think I can answer this one.
Gon's transformation in Hunter X Hunter... Burning the boat in One Piece... Final game in Eyeshield... Thorfinn's failed revenge in Vinland Saga... I'm not good at this.
Book that almost made you quit comics?
I kind of did quit comics, though. It was not a particular comic, but the fact that I was a child and didn't understand all the crossovers and content missing from what I was reading in both Marvel and DC things. Infinite Crisis confused elementary school me.
I was attracted to the way Japanese comics had a consistent writer and artist, lacked the baggage of a connected universe or events, and the consistent release schedule (for the most part). Since being introduced to Image, though, I love Japanese and Western comics equally (and for completely different reasons).