a lot of ppl prefer gold class btween the two due to better cleaning ability

UWW is a lil bit lacking in that area

some more GC is cheaper

GC is more expensive is because its in a bigger bottle.
Wash n Wax is gentler thus lesser cleaning ability.
This is a good choice if you're on a weekly top up wash plus quickwax.
GC doesnt have any waxing ability. It cleans better for a better prep for compound/polishing.

Detailing, its all about the prep before doing anything else.

I'll say go for Wash n Wax if you're just planning on washing only.