I haven’t done Afan, only trailcentre I’ve done that’s comparable with GT is CYB. Tons of riding, loads of variety, also you can hit it pretty fast first time as the design and sightlines are excellent. Not very technical in most of it but there are bits to spice it up, means it’s very all-skills as most folks can get round the red but better riders can up the speed and it becomes a different thing. It is ace.
Innerleithen’s a bit of a one-trick pony on the red (pedally, wide, jumps drops and drops) good for a visit though if you like that. Always think it’s weird that people call GT a bmx track when it’s far more natural feeling in places and far more varied. The black spices it up with some slower rocky stuff. But the off-map and dh stuff is stunning- almost all the good riding at innerleithen isn’t on the trailcentre route, and that’s what makes it so brilliant.