Right then..
CyB = good range of trails and terrain. Yes it gets a slating, especially since it’s “tarmac’d” a lot of the descents but it’s still entertaining, esp if you like Llandegla etc. Dragon’s back & MBR routes are both good mid distance routes. The Beast is a long distance combination of the above 2. The Tarw is good in places but is showing it’s age a bit with a lot of fire road stuff. There’s a shorter route for more novice riders too if you’re a mixed group.
Machynlleth (Climach-x) = good short blast with nice singletrack and great views. Not much technical stuff…. except the last descent which is long, gnarly and will have you going back up to do it again (there’s an un-signed short cut back up to the top)
Nant-yr-Arian = one of my favourite places to ride – if the weather’s good, you get a real sense of being out in the middle of nowhere, especially if you do the longer distance tracks (The old MBR killer loop that heads off the continental trails is the best for a real variety of terrain from man made singletrack to rocky forest descents)
Penmachno & Llandegla – you’ve done them so know what to expect 🙂
Marin – a good mix, great views and some good descents. Again, this trail is showing it’s age a bit though with little technical riding.
All the above is IMHO of course 😉