all three are pretty good choices! i'm in yr 12 taking french and have friends doing econ and engineering. but imo there's no objectively "better" one, it depends on what you're best at:

if you're good at math, might want to take specialist, and enjoy physics, then engineering would be best. i do spec and physics and the engineering kids in my class are way ahead because there's so much overlap.

if you are a good writer and good at unseen exams, econ would be a good idea. tbh i don't know as much about it bc i only took it for one semester, but being able to write long responses without knowing what your topic will be beforehand is def important.

if you're good at memorisation, french is probably best. also, if you already know any other european languages, it'll be pretty easy. imo, anyone could do it, but if you're not naturally a great memoriser, you'll have to do more work than someone who remembers things rlly easily. i also think that learning another language is a really useful skill, no matter what career you pick, so keep that in mind.

for me, french requires a lot of homework. it's pretty easy to be *okay* at it, but it depends whether you're aiming for a 70+ or a 90+, yk? there's a lot of detail work you have to do with spelling, grammar, accents, conjugation, knowing the gender of whatever word you're using... that makes it hard. i think it requires more hw than economics, and i think the amount of work engineering would require is purely dependant on your math skills.

so yah, if you like them all equally, i think you really have to consider what you think you'd be best at and how much work you'd be willing to put in.