Spanish, French and Italian are closely related, so if your child wants to learn multiple languages, any of the three would be helpful toward the others. I agree that French pronunciation is more difficult, but so many words in English come from French that vocabulary is relatively easy.
Regarding JonLaw's comments on Spanish, I couldn't agree more as far as its ability to increase your income, at least in general. I did get my first two jobs as a result of my bilingual abilities, the second of which was in the financial sector and paid quite well (this is probably an exception which confirms the rule). However, I now translate documents for my church, kids' school and pretty much whoever asks on a volunteer basis.
That said, living in the SW US, I use my Spanish almost daily, with the housekeeper, the lawn guys, the employees of our contractor, the lady who sells balloons at the grocery store. I may not any money this way, but I'm sure I've saved a fortune just by being able to communicate with the people who are actually doing the work, thus cutting down on mistakes and misunderstandings.
With my own children, we are starting with Spanish (but this is because we're already a bilingual household) and will add French when they are a little older, so they will be able to order in our favorite restaurant.
