I also looked last year (before I bought my second GTD) at the Ford ST line. Like everyone says, cracking spec, and very price competitive, especially considering the huge discounts I was offered - a fully specced ST3 (petrol) came in at over £5.5k less than the similarly specced GTI I was looking at, at the time (manual vs manual for a price comparison).
For me it was a couple of things that put me off. 1) Resale value - even with the bigger discounts offered the 3 year residuals were much worse than a Golf b) no Auto box. I know for some people that wouldn't put them off, but I love the DSG's on my last 3 VW's and wouldn't go back to a manual. I know the diesel ST now has an auto version, but not the petrol. and lastly c), Whilst I do think the general styling of the Focus is spot on (especially the Aston Martin-esk front and grill, but I've never liked the rear end of the focus which I just find to fussy with it's high mounted rear lights which heavily scallop in the rear wings. It's a personal thing but I think the Focus is better looking from the front than a Golf, but in all other angles (profile and rear), the Golf is much better.
Didn't find the interior or infotainment systems that much worse in design and build to the Golf to be honest, but I think I do overall prefer the understated looks internally of the performance Golf's over the performance Focus's. No doubt it is a very good car though. VW need to up their game to stay ahead of the pack
Can't say I've ever considered the new Astra, but it is quite a pretty looking car with good spec, but no idea what's it's like to site in or own though ?