Design is a form of art and as such it's evaluation can be highly subjective, however there are some concrete measures of what separates the good from the bad or what works and what doesn't. When it comes to branding and logo design here are a few questions you should be asking.

Is it simple?

If in sharing the logo concept with someone you have to explain it, then it's probably too complicated.

Is it memorable?

Does the logo look generic or unique?

Is it timeless?

Will it work with a variety of future design pieces and campaigns, fonts, images and colors etc?

Is it versatile?

The logo should be just as clear and readable on the footer of a black and white zerox copy as it is large and in full color.

Is it relevant?

Does it tell you anything about the industry / vertical market or organization it represents?

Feedback is a huge part of logo design. I recommend email surveys of your top finalists before choosing and commiting to a logo. peer review can be invaluable and easy way to ensure you are choosing a brand that will represent you well for years to come!