I have some major issues with both films, but A4 actually has more scenes I enjoy or that I feel properly convey horror - and of course Weaver was awesome as always, but especially so in this Alien-hybrid persona.
Of course A3 is a better FILM on a solely critical basis. However, A4 has these scenes that I love:
What's-his-face studying the Aliens up close through the glass - love that whole scene (too bad the Alien design sucks)
The unimaginable evil of humans submitting other unwitting humans to be chest-bursted; fits in with the dark universe perfectly
The Ripley clone scene was horrifying - again played perfectly by Weaver and again showing the monstrosity of people like Wren
Basketball scene
Aliens escaping scene
What happened to Purvis was pretty horrible too