If I'm being honest, I choose to avoid both of them.
However, on the odd chance that I do decide to eat one, here are the following conditions followed by some pro's and con's.
1. I have received them as a gift and it would be impolite not to indulge myself.
2. I am starving and there is nothing left in the kitchen to eat.
3. I am stopping by a service station or small outlet and decide to grab a small snack.
4. I have had a shitty workday, and have decided to eat everything in the house in self pity.
Pro's and Con's
Pro - Both provide a sticky, tasty surprise you just really can't find anywhere else.
Con - This 'stickiness' gets in your teeth and can provide for some embarrassing situations in front of others.
Pro - It is a quick refreshing snack when you're on the go.
Con - It is common that after eating these chocolates that your mouth becomes dry, providing minor discomfort.
As I already stated, I don't typically enjoy either of these sugary treats, but if I had to choose, I would give Mars the +1.