Recirculating BOV, trim sizes?

[Bleak]

http://www.frsport.com/index.php?target=products&product_id=1309

Going to be ordering one of these this weekend.
What size should I order?
They come in 19, 29, 32, 34mm.

Or is it up to me, depending on the material I use to recirculate?

 

[robertftw]

It is up to you, it is just the nipple size that changes not the threaded side.

 

[Bleak]

It is up to you, it is just the nipple size that changes not the threaded side.

I know, I was just wondering if there was a suggested size to run, the bigger the better or any advice like that. Or if it was simply up to me, and the size really doesn't matter.