Downloads the entire blockchain.
Ranked in these QuestionsQuestion Ranking
Pro High level of security
No third-party has access to your private keys. Private keys are both generated and held locally. Additionally, as it is the official client, it is the most actively peer reviewed wallet.
Pro Open source
Being open source allows the client to be peer reviewed. It also allows you to download the source code and compile it yourself in case you're worried that the source code is different from the distributed version of the application.
Con Takes up a lot of space
As of December 2015, the entire blockchain is over 50GB. The growth rate has been more or less linear for the last year when it grew in size by about 25GB. Thus it's reasonable to expect the blockchain to grow to 75GB by the end of 2016 and so on.
Con Initial sync takes a lot of time
Since the wallet downloads the entire blockchain the first time it loads, which as of December, 2015 is over 50GB, it can take a long time to download.