Research says the
FR-S will baby.
If you aren't planning on having a second child right away, you could easily get a couple years out of the FR-S before it became an issue (I'm assuming it's also not your only vehicle between the two of you).
You're going to take a hit on the FR-S no matter what, but you're taking the biggest hit in the first year. It'd need to be a helluva discount on the next ride. From a fiscal standpoint, taking on a higher payment isn't necessarily the best idea.