As a woman set to begin a foursome with another couple do you stare at the other guy's penis comparing it to your husband or do you stare at the other wife's breasts?

.......generally people who aren't new to these experiences don't compare at all, they appreciate.

Everyone is unique. A guy can come standard issue and destroy a woman. A guy can come on the bigger end and just be a jackhammer and no one asks him back.

A woman with enthusiasm is more fun than a model.

Plenty of people are pretty until they talk.

Just have fun. More people means more time in support roles, but then more attention on you when it comes around. Don't hold back and don't be embarrassed.

My wife has always told me that all cocks are basically the same. All about the same size. All taste the same. All feel basically the same when they are thrusting in and out of your cunt. So first time she is seeing another couple nude she likes to size up the other wife's tits in comparison to her own.

As a man I stare longingly into the other man's eyes while I fuck his wife

Both!