7x42 or 10x50 porro-prism (the classic dog-leg shaped model in the picture) can't really be beaten for value for money.
You can make them with all spherical easy to manufacture elements and the prisms are relatively insensitive to errors.
They are a lot simpler to make than more modern compact designs so for the same money you (should) get better units.

After that it's all down to manufacturer's quality.
The main thing to look for when testing them is chromatic aberration - especially lateral color. Look for rainbows around the edges of high contrast edges especially near the edges - geometric distortion isn't usually important with visual use.

Remember that a German sounding name doesn't mean they are made in Germany (or Austria) and any extra 'features' like colored lens filters or built-in compasses usually mean poor quality.