From the beginning Debbie and Melanie were my favorite female characters and that never really changed. I adore Daphne and think she is a fabulous friend to Justin, but she doesn't really have her own story.
To me, Debbie is just made of love. Sure she loves loudly, but also completely and with her whole heart. She can't be anyone but who she is. A lot of her faults stem from that same need to speak her mind and do what she thinks is best for those she loves so even when she is wrong it is easy for me to forgive her. I also think it takes a lot of courage to live with your heart on your sleeve as much as Debbie does.
I started watching QAF at the height of my fertility problems so it was easy for me to identify with Melanie and how she could totally love and adore Gus, but be very frustrated about having Brian as the father. I love that Melanie is strong and smart but also very loving and nurturing. She is also a great friend to Ted and Justin. I also appreciated a character (especially in S1) who wasn't in awe of Brian and could point out his faults without making excuses for him. Debbie and Melanie both get a lot of fandom hate for not worshiping Brian, and that just makes me extra protective of them.
NY already mentioned my struggles with Lindsay. Some of them are related to Melanie and others to Brian. In general, I find Lindsay a little unwilling to compromise and a bit manipulative. But she is also loyal and loving and works very hard to create a family that is full of love. I love how she takes Justin into her life, I love her proposal to Melanie, and I love that she never gives up on the happiness she knows she and Melanie can have.
Jennifer is a character I just can't get a handle on. For all the times that I love her, there are other times when she frustrates the hell out of me. People have mentioned some of the great moments of support she had with Justin-chasing after him at school, standing up to the principal etc. And I think because of those, the times when I see her hurt him really bother. Maybe when my kids are older, I'll be able to understand, but considering she didn't know Brian at all, turning Justin over to him (maybe in hopes Justin would come running home?) seems really insane. And the scene at Molly's birthday party absolutely breaks my heart. I also can't believe there was no middle ground between Brian not seeing Justin at all and her turning Justin over to him again in 202. It might be because Justin is my favorite, but I feel like when Justin is too much trouble sometimes Jennifer gives up too easily. I write a lot of Jennifer drabbles trying to understand her and I try and focus on the times when she is awesome because I know she loves Justin. I also love her and Debbie as friends.