I think I'm coming to the conclusion that F is always better, even with a connection - at least for me.

Yes, you can get extra legroom in E+ on UA, but then there's still the issue of the shared armrest, which can drive me a little nuts, especially if I'm next to some burly/beefy guy.

And then there's the possibility that you might get stuck on the tarmac for some reason. Again, it's better to be stuck in F than stuck in Economy.