If you're going to be handling http requests it's almost a given you'll be using AppEngine rather than Cloud Functions. Still "serverless" but more tools and languages to choose from.
Not the flexible environment iirc. Which is basically the reasonable env to expect, now. Standard env has some aging issues that keep getting worse. most notably jvm 7, if that’s your poison, but just all round crippled env lacking standard libs and with lock in substitutions.
> If you're going to be handling http requests it's almost a given you'll be using AppEngine rather than Cloud Functions
Why? Cloud Functions support HTTP.
I mean, if you can stay within AppEngine’s free tier quotas, there's a clear reason to use it, but otherwise it would seem to be a matter of weighing pros and cons, with HTTP alone not deciding that you should use AE over CF.