Ichiya was reigning supreme as the ultimate plot device until Wendy in Alvarez walked in.
Erza's POF is not a big deal, it's part of the theme of the series and she's a main character. If you can't handle POF, then don't read Fairy Tail.
Lucy feels more like a main character than anyone else in the show. We don't even know as much about Natsu's personality and what goes on in his mind unless he's in a fight. I feel like that's something that should be tackled. I almost feel like he needs his own spinoff. Having a narrator kind of doesn't help us know the supposed main character of the series.
Hypersexualisation is too much in this series that it sometimes cancels out the support for feminism through Erza. This sexualisation should be lessened.
Ultear, Mavis and August were the most well-written characters in the series. Out of the inner circle of main characters, I think it's Lucy. Thinking about it now, she's probably the one I enjoy the most with the exception of maybe Happy and Erza at times.