I need to work on my x guard set ups. I focused on my passing and top game this past year and have neglected other parts parts of the game. At least I know what to work on now. :)
Every time I pull guard from a standing position, I've always, literally always pulled full guard or at least tried to. I've never had the idea to pull someone into butterfly but I love butterfly guard and I feel kinda retarded for not having thought to before. lol Thank you so much Louis! :)
I've been playing shin in de la riva/shin in sit up guard (whatever you wanna call it) a lot lately, even when guys start w/ one knee up, some fun sweeps to work on or can go to single-x or x-guard easy
How to do it: http://www.youtube.com/watch?v=zfmmzQnmbT8
How to stop it: http://www.youtube.com/watch?v=nH2eWhg9odU
IMO the only real answer to your question is "the guard/sweep that your opponent is giving you". Open guard/passing the guard are easily the most complex and important positions in Jiu Jitsu. There's no such thing as getting good at one open guard because they all work off each other. If you're not working X, DLR, RDLR, Inverted, 50/50, Sit Up, Spider etc... your guard has major holes in it. The key is knowing how these guards intertwine. As far as I'm concerned, passing/sweeping should be 90% of your focus in training.
For me is X and 1 Legged X