Kournikova- I don't know much about her, but I watched videos of her playing, and I really liked her game. She was a really good doubles player though...so I can't really give an opinion. Surprised that she didn't win a title though.
Ivanovic- The way the media was hyping her up, I thought she would at least win 6 slams or something. To be honest, she was a great player, but she could never really challenge the top players playing at their best. In the AO in 08, the only big name she beat to get to the finals was Venus, who made a million errors. In the French Open 08, she was really good though. But she really only played Jankovic and Safina. People saw her win her first title though, and really hyped her up and thought she would win wimbledon. Now it's very doubtful that she'll ever win another title. But let's watch her play Clijsters in Madison Square Garden with her new coach-we'll see if she did something. Another dissapointing thing about Ana is that she's doing all the modeling stuff w/o the sucess and gets annoyed when ppl compare her to Kournikova. And, she's not doing much to build her game and confidence because she's not entering any small tournaments.
Caroline- It's really too early to see. She had a pretty easy draw at the US Open, but she did challenge Clijsters. But to be honest, she really relies on her opponents errors to win. When she played Peer in Dubai, Peer was dictating. There aren't too many top players who let Peer dictate them. So yes, she's overrated for now, but she can improve a lot...esp if she changes her mindset about attacking.
So my opinion is Ana>Anna>Caroline...just because Caroline hasn't had much time to prove she's not overrated.