By far Sasha (but then again we are dealing with health issues with her). If she even looks odd we go to the vet. Then again, she can't tell me what's wrong, so better safe than sorry. If she could say, "No Mom, I'm really fine. I just got into the trash when you weren't looking and now my tummy hurts. Don't worry though, I didn't eat anything poisonous." Then it might be a different story.
I only go if I am really really really sick. I have a high pain tolerance, and rarely do I let being sick stop me from doing what I need to get done. When it gets to the point where I can't hardly get out of bed; then I go.