Like I once said on the thinking thread, I think OITNB is great, but I wouldn't consider it Netflix's best original show, mainly in terms of plot. This is just a personal opinion, of course.
I am still watching Season 3, if I must be honest, and am finding it to be weaker than the others. I'm kind of 'forcing myself' to end it so that I can finally start watching the new season.
In terms of favourite characters, I'll have to say Alex, Piper, Nicky and Red. But, since I'm still delayed on the show, my favourites may change.