Which should I use? Tile background or sprite?

Here's a screenshot of my game.

<img src="http://i.imgur.com/KLDbx.jpg" border="0" />

And here's another piece of decoration I plan on throwing into the stage.

<img src="http://i.imgur.com/oHSYj.jpg" border="0" />

Should I use tile background or sprite object for that thing? Which is better for processing and video and RAM and all that?

I'd just use a sprite. Tiledbackgrounds and sprites use the same amount of vram. Sprites render a tad slower, but it's insignificant since you are getting 60fps. Plus sprites allow you to rotate/scale/shear/mirror the image easily.