Strongest is such a subjective term.
In terms of raw strength, Tsunade and Sakura are definitely the most powerful. However, neither are very good at applying their offensive capabilities in combat. If you think about it, Sakura really hasn't been able to land solid attacks on an opponent without somebody else assisting her. Tsunade isn't much better. While she was strong enough to crack Madara's Susanoo and land a potentially fatal blow, it ended up just being a clone.
In terms of offensive capability, I would have to pick Konan or Temari. They have shown more combat potential than probably any other kunoichi in the series. Konan was able to go up against Obito in a one on one battle, and made him sacrifice one of his eyes after pushing him to his limit. Temari is probably the more likely pick, though. Even though we haven't seen much of her combat potential, she definitely puts most of the other shinobi to shame. She is also considered one of the best Wind Style shinobi in the Alliance.
In terms of versatility, I would have to say Tenten or Ino. Tenten is essentially a master of seals and weapons use. This means that she can be used for mid- to short-range combat and as a supply pack mule. Ino on the other hand has made huge improvements since the time skip. She is clearly very capable at both relaying information and sensing chakra.
Overall, most of the female characters in the series are lackluster at best. Tsunade and Sakura have huge amounts of power, but cannot apply it appropriately in combat, and are thus extremely limited (albeit talented) medical personnel. The rest of the female Leaf shinobi are just watered-down versions of their male counterparts. Thus leaving Temari as probably the most capable kunoichi of the series.