I think they are all strong in their own ways,but Bella I think has more strength both mentally and physically.I mean look at what she had to overcome both as a human and as a vampire.

Bella has become much more powerful both mentally & physically after her transformation.

I found her to be strong even before her transformation.She had an inner strength in her that made her strong.

Rosalie is strong physically but more importantly mentally. What she had to go through with Royce and overcoming it is probably the hardest thing she had to do, which makes her a strong person. Bella being strong? That's ridiculous because she relies on Edward all the time - her life revolves around Edward. Nothing else matters to her.

I disagree with your last statement Emmalie1935,that she relies on Edward all the time and that nothing else matters to her.Renesmee and her family and friends matter to her,not just Edward.What about when Edward left her in New Moon and what about in BD part 1 when she found out she was pregnant?She even said to Jacob:I'm strong enough,and she proved it.You are entitled to your opinion,but the last statement I disagree with.