Personally I would go from French to English but not the reverse. There is a lot of conditioning (possibly the most accurate, if a little extreme way to describe it) which goes on in the early years which teaches the 'right' way of doing things such as writing and formating and the whole system penalises rather than encourages, which can be very demoralising for a child used to the more nurturing environment typically found in English schools. There is also quite a lot of learning by rote which, if you haven't done, causes issues at higher levels when you're supposed to have things at your fingertips. HOWEVER I don't find that it produces brilliant thinkers or very original students. Getting my classes to express their opinion is a nightmare but they will happily quote other people's. Asking them to reason something from cause to effect, and vice versa, results in blank faces but if I tell them they'll be able to parrot my reasoning back to me. I guess what it lacks most of all is cross-application of skills.
The English system values individuality and creativity much more than the French, which achieves generally excellent results by enforcing a good work ethic and a strong foundation in literacy and numeracy. You are expected to work and work HARD but that focus on application also provides a rounded education of good standard up to the age of 18 - even if you doing a bac S (sciences) you have to continue with a foreign language etc. I think the English system specialises too early.
I would rate English universities, in general, above French ones - French universities (with the exception of the grandes écoles which are a totally different ball game) are non-selective. If you pass your bac then you can go. This leads to a very wide range of abilities and makes teaching quite difficult. It's also not anywhere near as enquiry focused.
If you are considering the move I would sign up to the CNED and get the homeschooling materials so your DC are up to speed with what the French expect.
FWIW my plan, as someone currently working in the education nationale, is French system to age 11 and a more English approach at secondary level, ideally at a bilingual school sous contrat with a strong track record for the IB, failing that a British secondary with an IB option or an international school.
Overall it depends on your definition of better really...