All of Them
Let's look at it from each characters perspective first:
- Cersei - She is controlling and the current Queen. If she is to meet with them she is going to do it on her terms and that is at Kings Landing. She holds power at Kings Landing and is more protected there. She also probably chose the Dragonpit for the reason Dany says herself "This place was the end for my family." It is to show Dany that even great dragons can become small and weak and be overtaken by the next generation.
- Jon - He needs the support of everyone he can if he is to win the war over the undead. If he invites Cersei to him she will almost certainly decline suspecting it is a trap. So he takes the evidence to her which makes complete sense as it will also make her trust him a little bit more.
- Dany - She knows if she asks Cersei to go to her she will say no, she knows if she doesn't go to Cersei she won't help as the two don't trust each other at all. But Dany going to Cersei will at least show a bit of trust between them.
Also, as @Skooba, says:
It was a pretty good place to compromise on IMO, outside the city proper so Jon/Dany don't feel like it is a trap, but close enough to the city where Cersei can feel safe and easily bring her guards.
However, we know the actual meeting was organised by Tyrion and Jaime when they met in secret. The details of their conversation isn't gone into in detail but we can speculate that it was organised there and then.
The conversation later on between Jaime and Cersei goes into more detail about the fact that Dany wants to meet with Cersei but that's about it:
Why are you here?
I met with Tyrion.
What did our brother have to say?
Daenerys wants to meet.
To discuss her surrender?
To discuss an armistice.
She's just won a great victory. Why would she want a truce now?
Because an army of dead men is marching on the Seven Kingdoms. Tyrion claims he'll have proof.