Although both have their advantages I like the ones that are just being opened. I will be able to see how everyone plays and remember some of the important information received from certain plays/players.. Most of the time when I sit down on an existing game idk who is tilting, had multiple buy ins, etc.. Yes a couple orbits will help me understand the dynamics of the table but a new table is just my preference.

I prefer an existing game since usually the ice has been broken in that some players are already losing and starting to play bad and chasing their losses as a result. New games tend to be a lot tighter.