Reviews aside, I'd say the Focus is more premium than the Astra, the best to drive of all of them imo, and rarer. I quite like the megane and you can pick them up for an absolute song. Must it be hardtop? A4 cab's are excellent cars.
I used to sell cars so you could say I have a little knowledge around the subject. It'll always be a trade off. They're both heavy. The Astra may be slightly better t drive but the VW will ultimately be more reliable and hold value better if serviced properly. Beware the 2.0 Tdi version if offered. They go through injectors. I'm on my 5th Golf. I've owned a lot of cars besides. What amazes me is what DOESN'T wear out on a VW. What yosuspend in purchase price you'll save on consumables and items that wear out, like suspension components.