I've been avoiding posting in this thread for awhile because for some strange reason I'm finding it hard to give a conclusive answer to this question. Unlike with male wrestlers where I have a definitive answer in Shawn Michaels, with the diva's it's a bit tougher to come up with one. I've tried to do this by breaking it up into sections; favorite in-ring competitor; favorite on the mic; favorite in my pants; and then combine them altogether and see who comes out be even then it doesn't feel right. So lieu of actually answering your question, I'm going to throw out a bunch of names that really stick out to me.
The first person who does, and this is no surprise looking at my post history, is Eve Torres. <3 Eve. One of the most beautiful Diva's they've ever had in my opinion (I've got 183 pictures on my laptop as evidence), but I'm not shallow enough to judge solely based on looks (granted, what makes someone attractive to me isn't solely looks either) because if I did Maria Kanellis would definitely be getting a mention and she isn't. Eve is also really good in the ring. Her match with Kaitlyn at the Raw 20th anniversary was my favorite part of the show and I enjoyed that match entirely because of Eve. She's also had several of my favorite diva matches period, I loved her series with Beth (who I won't mention but she's awesome too). Her mic skills are admittedly the worst part of her arsenal, but by diva standards I think she's really one of the best (though I can think of a few that are better than her) and she also obviously kept improving on them so yeah, it's hardly a negative by the tailgate of her career.
Okay, I'll keep the others brief. Melina & Trish Stratus/Lita are the other ones that immediately pop into mind. Melina for awhile was my favorite but that's change over the past few years. I really can't comment on her mic skills as I don't recall her getting all too much time on the mic to showcase them, thus the tragedy of being a female wrestler, but from what I can recall she was okay. In-ring though she was great, having several matches I really loved (like her match against Michelle McCool at Night Of Champions 09 & the I Quit against Beth Phoenix). Trish & Lita are obvious but who I prefer depends on criteria. Lita will win if the criteria is in-ring ability, Trish wins in the other two categories and kind of easily but I do tend to evaluate the wrestling portion higher. Finally, shout out to Mickie James.