I would like to add some more points and try to point which was the Borden who loved Olivia and the Borden who loved Sarah in each scene.
I loved Sarah. He loved Olivia. says a lot of things in the last scene of the movie. BORDEN WHO LOVED SARAH loved Sarah and BORDEN WHO LOVED OLIVIA loved Olivia. Now how can we say that the living one is BORDEN WHO LOVED SARAH? Before Fallon i.e. his twin brother joined him in the movie, he fell in love for her and he said "I loved Sarah"
2) BORDEN WHO LOVED SARAH is the Borden who took interest in Sarah and went to her house.
3) Remember when Borden who loved Olivia gifted her the key, the conversation was like:
I asked you last week
You caught me in a wrong mood
But you wont ever
I am gonna have to change my mind, aren't I?
So it is presumable that when she requested for it, it was BORDEN WHO LOVED OLIVIA, who was in the wrong mood. But as soon as he told BORDEN WHO LOVED SARAH, he took no time in arranging a house.
4) In the party after Borden was compelled to give the keyword "TESLA" to Angier, he was acting very bad to Sarah, this was probably BORDEN WHO LOVED OLIVIA and Fallown was there BORDEN WHO LOVED SARAH because When Sarah requested him to escort Olivia to home, despite Borden who loved Oliviard said
Don't ruin this evening he stood up and took Olivia home. After that Borden who loved Oliviar quarreled with Sarah, which proves my opinion. At the end, Sarah said:
No Alfred stop. This isn't you. Stop performing.
5) Olivia came to BORDEN WHO LOVED OLIVIA, with whom she fell in affair with.
6) When Borden who loved Sarah was going to take them for the zoo, he said to Sarah
I love you. I will always love you.
and Sarah said:
You mean it today.
This is BORDEN WHO LOVED SARAH in action.
7) In a scene where Borden was talking to Fallon, he said:
And, uh... Sarah,Uh, at least she knows
that something is not right,
Talk to her, just
convince her that I do love her.
Here BORDEN WHO LOVED SARAH is talking to BORDEN WHO LOVED OLIVIA. We get the proof in the next scene, when he meets Olivia and she kisses her and he said:
It's nothing. It's just that
sometimes it seems wrong.
8) Before committing suicide in the last fight, Sarah was talking to BORDEN WHO LOVED OLIVIA and Fallon was the BORDEN WHO LOVED SARAH who took their daughter aside. That is why,
When Sarah asked "Do you love me?"
No, not today
9) In the last meeting with Olivia, he said he loved her and he did not mention Sarah's name once. that is the BORDEN WHO LOVED OLIVIA. Olivia was upset with the fact and said
It is inhuman to be such cold.
10) And the Borden who loved Sarah lived and who was hanged was BORDEN WHO LOVED OLIVIA, who said
I am sorry for a lot of things. I am sorry about Sarah. Did not mean to hurt her. You two live for both of you.
That means the living one was BORDEN WHO LOVED SARAH and the hanged one was BORDEN WHO LOVED OLIVIA.
11) In the opening scene when Sarah informed about her pregnancy to Borden, it was who loved Olivia, that is why he said:
We should tell Fallon
So these are some other points where we can differentiate between them.