First class all the way! Bigger seat,less crowded and cleaner bathroom.

I have never been on a French train that had different food options depending on which class of seat you were in.>

I have been on TGV trains where only in first class could you order a meal to be delivered to your seat - not sure this is the case anymore but once was.

<If I traveled a lot by train on business or something, it wouldn't be worth it, but when I'm on a vacation I take only once a year or something, it's worth it.>

I agree with Christiana's take - on a rare holiday why not splurge a bit and go in style? If regularly commuting it may be different. And this is why constantly we have Europeans exhorting Americans on holiday not to waste money in first class, etc. - they just cannot put themselves into the place of folks on holiday take a few train trips. Yeh you could stay in Formule I hotels too and they are basically really comfy - but tourists do not - apply the same criteria to rail travel on holiday IMO