Why did Miranda Tate choose to (spoiler) with Bruce Wayne?

To fully gain his trust. She wanted to kidnap Bruce when she asked him to go away toghther in her private plane but Bruce declined.

I'm sure Bane really appreciated that step of the plan

Did she really need a reason?

Besides, it made her cover perfect, the person he's most likely to trust.

So that when Nolan's knight was recovering in the pit he'd never suspect her of being involved in Bane getting his hands on the fusion reactor even on a subconscious level, despite the long sequence of coincidences that pointed in that exact direction. As Gordon points out to Blake, detectives aren't allowed to believe in coincidences, so 'The World's Greatest Detective' couldn't be allowed to spot them, could he? This was essential so that her plan for Nolan's knight to escape from the pit, travel back to Gotham, save Gordon and free the cops, lead a suicidal assault on Bane's vastly superior tactical position, defeat Bane in hand to hand combat and then hand her a shotgun and turn his back on her so she could stab him in the ribs and explain that she was actually not 'Miranda', but the evil Talia, would work.

Or, considering that 'Miranda' and 'Talia' are written more like two separate characters than two different identities, maybe 'Miranda' had the hots for Bruce, while 'Talia' hated him. Maybe they were actually twin sisters, like Bale's character(s) in 'The Prestige', perhaps?

Read an interview with Marion Cotillard recently in which she herself admitted that Talia's death scene sucked. She also had bad things to say about an unnamed 'director' who used all of her worst takes in the last movie she made with him; she hasn't worked with Nolan since 'rises', has she?

An opinion is not offensive just because you do not agree with it.

Hollywood needs the obligatory romance scene