I got 50 respondents now, plus myself, and so it is time to post the results:
It seems that most of the respondents definitely enjoy sex with multiple people and most would like all their holes to be fucked at the same time.
Male ass and mouth seem to be most popular for double stuffing, whereas women prefer their pussy to be double stuffed in favor of their mouth.
A mix of the sexes when engaging in group sex is definitely preferred by all, except for the respondents who are gay.
Thanks a lot for your responses. Of course, you are welcome to keep responding. If I reach 100 I may do another analysis.