Definitely Knotweed. Or Scotchbroom. No, Knotweed.

Hey, wait! Don't forget Johnsongrass, kudzu and crown vetch!

Knotweed - hands down!

I vote for knotweed, or as I call it, Angry Weed. When we moved in 8 years ago we had a hedge 200' long x 5' deep surrounding our yard. As we pulled it it seemed to grow thicker, stronger and faster. Luckily now it is mostly gone, and we just pull sprouts once every now and then.

Rhamnus cathartica, common Buckthorn. Around here it is the weed, all due respect to garlic mustard.

creeping charlie. Sorry, but I've seen this one grow into a dark shed, turn white and try to tie down the lawnmower.

Knotweed is a tough customer, though.

Between creeping charlie and knotweed, there would be no winner because Knotweed would take the high ground and deep root zone and charlie would take the low and shallow root area. They wouldn't even notice each other (but nothing else would survive.

~Chills

Rosa rugosa. The others are very easy to combat compared to this one that spreads from seed and root.

Dilute at the rate of 1 part herbicide to 40 parts of water for treatment of most prenial weeds and 1 to 40 for treatment of hardy invasive plants like Japanese Knotweed and 1:20 for Ivy

Here is a link that might be useful: Knotweed Control

Knotweed - nothing at all will grow under it, even other weeds.