I wouldn't look at $50 more or less. On the total of this trip, it's nothing. I've never heard of XL Airways and I work for a European (half French) airline ;-) If the timing of this flight works out the best, look at some reviews online.
Personally I would go with BA as well. As
@dolewhipdreams says most time in Paris. It's going to be a short trip anyway, and by getting there early you could take things slow. If you do not sleep on the plane, you'll be exhausted. By getting there early (and hopefully have a room ready early as well), you could unwind in the hotel for an hour or two, and get a refreshed start in Paris.
Also if BA is in your Frequent Flyer Program, I would definitely go with this one.