I have 3 players that are basically, fully developed. I will have room on ML roster for 1-2 of them, and then trade the remaining player(s) for other needs. I have my main lineup/stars. These will be 300-350 ABs guys baring injuries to other players. I play in a fairly neutral park and value OBP and vsR a little more than power. All 3 are similar in vsR.

Who do I keep? Who do I trade?

https://www.whatifsports.com/hbd/Pages/Popups/PlayerRatings.aspx?pid=10351552 https://www.whatifsports.com/hbd/Pages/Popups/PlayerRatings.aspx?pid=10186085 https://www.whatifsports.com/hbd/Pages/Popups/PlayerRatings.aspx?pid=10500645

Thoughts

There are two considerations here.
1) Will they be getting most of their ABs against RHP, or LHP? If your starting lineup wants to rest against RHP then Gil gives you the platoon advantage and that, with the slightly better VsR, makes him the best choice to keep. If the lineup wants to rest against LHP then Papelbon or Booth is better. If some of both then I'd keep Gil and one of the other two.
2) All that said, unless there was a major handedness issue with your lineup I'd probably ask the opposite question-- who has the most trade value?

I'd probably look to trade the one that got me the best return, or keep Gil and look to move one of the other two to keep righty-lefty balance.

I would not trade Gil unless you can get a very good return. If you can get a high potential young DITR for one of the other two, I'd try to go for that.