Well I only see a few lines jagged at the girls face/hair part. Other than that the lines seem okay.

I suggest putting something meaning full into the background - might work well with some garden-way (meaning brown ground, some flowers on the sides (or something green) and a bench maybe?). It will be diffcult to find it in the right perspective though - you might want to adjust the perspective (don't know if gimp or whatever tool you use let's you - but photoshop certainly has this perspective correction). However this might involve quite some work - depending on what way you chose to make it.

As for those characters - they look fine to me.

dS.

I'm going to say pretty much what's already been said, but hopefully it means you'll listen to all of us. White does not cut it as a background if the vector isn't amazing, and frankly, this isn't. In cases like this, where the wall is essentially a character or two stuck over a background, the background is your place to shine as an artist since you need to create it yourself. Ideally the background should stand alone as a decent [usually abstract] wall before the addition of a character, and I don't know anyone who would be okay with a plain white wallpaper.

The vector is pretty good, but it's still fuzzy, in particular the eyes. The shading on her skirt looks horrific because for some reason you've outlined it. This accentuates the sharp edges and make the shadows look blocky rather than smooth like on her sleeves. The same goes for their hair and his entire outfit. Redo the shading so it's like her jacket instead.

I can't critique the rest of your vector accurately because for some reason you thought it would be a good idea to cover up your work with your signature. Logos, I feel, don't belong on walls we submit to AP because we aren't corporate companies that need to identify our work somehow. A personal logo is no exception, plus it only makes you look conceited to think you should have a logo rather than just a small line of text. Your signature should either be at the bottom of the wall where it will usually be covered up by by the taskbar, or if you can swing it, subtly hidden in the wall itself, like along the edge of an arm or piece of clothing [for examples, check out walls by `kuryuki]. Covering your work looks stupid and isn't even a beginner's mistake because the idea is to show off your work, not hide it.

My advice is to redo the vector because the shading is horrible and the eyes are fuzzy. After that you need some kind of background that will compliment your characters. I don't know much about this series so I can't offer specifics, but a decent abstract background is never a bad idea if the wall isn't meant to be scenic. Finally you need to redo your signature, nice and subtle and without a giant ego-stroking logo covering your hard work. If you can't work it into the wall itself, just keep it along the bottom edge. Good luck.