I can't help with this one. I don't think I ever bought either kit. I do remember examining the Airfix one in the box, and concluding that it was an excellent one. (It was one of the last before the company got out of the sailing ship business - the same vintage as the Wasa, which, for its size, is surely one of the best plastic sailing ship kits ever.) I'm pretty sure the sails were vac-formed; I don't think Airfix ever used injection-molded sails on any of its kits, other than the tiny ones. (One partial exception: I believe the initial release of the Endeavour, the very first of the "Airfix Classic" series, had furled sails molded integrally with the yards, but subsequent issues of that kit had vac-formed sails.)
Pyro used to offer a Saint Louis of about the same size with injection-molded sails. I think Lindberg is currently promoting that kit as a "pirate ship," with the name "Sir Henry Morgan" or something equally ridiculous. I haven't seen that kit outside the box, but my guess is that it isn't serious competition for the Airfix one.
I vaguely remember a long-ago Forum exchange in which Michel VRTG, who knows the Heller line far better than I do, confirmed that the Heller Saint Louis was a different kit. But I don't recall ever having seen it.
Later edit: I found the earlier thread: ttp://cs.finescale.com/forums/632609/ShowPost.aspx . Sounds like the Heller kit scores over the others in having full-length guns on all decks, but in various other important respects the Airfix version is superior. Those descriptions would be enough to make me buy the Airfix one.
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