Of the 3 you’ve linked to, both the Giant and the Cannondale are very good bikes. The Mongoose is a massive unknown quantity, and has way too much travel (and weight I expect) to be any good as a trail bike.
Of the 2 left, the Trance X is a brilliant technical bike, they are highly underrated and really deserve a 140mm fork as the back end is so good. The Maestro suspension design also pedals very well, and helps the bike feel very lively.
The RZ140 is also an excellent bike. The extra travel will mean it noticeably have less feedback, but also be slightly better at swallowing bigger hits. Similarly good as an XC bike, perhaps slightly more suited to ripping down trails on balance though.
If you spend most of your time at Cannock, I’d buy the Giant, swap the 120mm fork for a 140, and go rag the hell out of it til you need to upgrade/replace anything else. I lve the Giant Maestro system, it pedals well, yet is also lively and still manages to smooth the trails out very well.
That said though, if you’re more intent on riding more DH trails with only a bit of XC, and you don’t mind a weight penalty, then the only real answer in your price range is the Specialized Pitch!