Ivanovic when playing well
Sharapova. Azarenka's a close second. Both are technically very fluid shots but Maria just hits a bigger ball so I give her the slight edge.
I'm no authority on net play (considering my own lack of ability and who my fave is
) but Radwanska, Errani, Serena, Kvitova are all up there.
Errani's is pretty solid and so is Kvitova's
Serena. It's always a shock to me when she misses one or doesn't put it away
Serena. She doesn't use it a ton but when she does they're measured to perfection.
Radwanska. Errani's up there, too.
Radwanska just because hers are so sneaky.
Serena. Raw speed and excellent anticipation make up for her sometimes-lackadaisical footwork. Plus no one moves forward better than Serena. Kerber would probably be runner-up.
Azarenka, Sharapova, Li Na when she doesn't forget her brain
All the top defensive minded players (Kerber and such) have to have great stamina to be where they are playing the type of tennis they play. Serena and Maria are really fit too and don't seem to get worn out after long rallies or lots of close matches in a row.
No one can touch Serena's will to win and, but honorable mentions to Azarenka (her self-belief and fearlessness when she's down is really impressive) and Sharapova (She's so resilient, and no active player has won more matches when playing like total crap than her)'
Also, I'll add:
Azarenka, Serena, Peak-Woz
Return of Serve:
Azarenka (Serena and Maria hit more menacing returns when they connect but they're far less consistent)
Edit: Add Venus to pretty much everything involving the net