Ero Sɘnnin's answer in How was it decided which warriors would go to Fólkvangr and which to Valhalla? seems to suggest that Odin gets to choose who enters Valhalla:
Valhalla is presided over by Odin, and to gain entrance to it, one must be chosen by him and his valkyries, the “choosers of the fallen.”
The only difference that is pointed out, is in the way that the dead are chosen to stay. Odin chooses for Valhalla, while Freya chooses for Folkvang.
This seems to be supported by Ero's (secondary) source: Death and the Afterlife, Norse Mythology for Smart People.
However, the Gylfaginning seems to be painting a slightly different picture (chapter 24):
Folkvang it is called,
And there rules Freyja.
For the seats in the hall
Half of the slain
She chooses each day;
The other half is Odin's.
Source: Wikisource contributors, 'Prose Edda/Gylfaginning', Wikisource , 29 January 2013, 01:25 UTC, https://en.wikisource.org/w/index.php?title=Prose_Edda/Gylfaginning&oldid=4271175 [accessed 22 June 2015]
The way I read the above quote, Freyja is the one who chooses, and Odin and Valhalla receive the "half of the slain" that's left.
Does Odin actually have a say? Or is Valhalla essentially the hall of Freyja's rejects?