Neither are perfect, but 1) is pretty close, while 2) has incorrect grammar.
1) The more attractive and informative an ad (is), the more effective it is.
You need to use the article "an". "Is" is optional. In this case, because you also use "is" at the end of the sentence, it is better to leave it out of the first part.
The more attractive and informative an ad, the more effective it is.