First of all nothing important, mostly stuff that's a distraction unless it becomes a need.
That said, using a static frontend cached on a CDN in general improves initial pageload and cuts down on traffic to your server by a lot. Netlify makes this easy if you want to use React on the client (with NextJS).
With AppEngine you get direct access in one console to all the bells and whistles of Google Cloud, basically the same as the other infra giants. AWS has even more bells and whistles but I find its console more annoying.
You can always add Cloudflare to the mix to cache static assets. This change is additive meaning you can start with a single Heroku deployment and if static asset traffic becomes an issue, you can create a Cloudflare account, configure DNS and be done.
Well if you're deploying a static site they are the same, but that's still not the whole picture. They have support for lambda style "serverless" functions and Fauna DB[1], and can bundle functions with apps automatically for some tools like Next.js to do server side rendering for dynamic routes[2]. So while they don't support quite the same level of custom stacks, backends and DBs, they do provide tools that enable full stack applications.
