I agree there's a big lack of good quality Chinese takeway/delivery in the area.
I'm a big fan of Good Earth, and that's my standard go-to. Its not cheap though!
One tip for Good Earth Restaurant - they have a proper restaurant (near Wandsworth Common) and a Good Earth Express (just for deliveries/takeaway).
I find that the quality from the Good Earth Restaurant is much better.
If you ring them up, they'll happily deliver locally. Free delivery too, over 20 pound spend. Only thing is they're not available through any of the apps, so you have to ring them to order and pay in cash on delivery.
Another place I love for takeaway/delivery - Pho Ta. Its Vietnamese, not Chinese, but they do amazing pho noodles and at very reasonable prices too. The soup is actually super hot when it arrives, which is the secret to great pho. They're available on the Just Eat app.