I had problems trying to sync my Ethereum Wallet for over 2 weeks, so I decided to try Parity instead of Geth. I originally started with version 1.2.4, but then Parity was exploited. Thankfully, these issues were addressed in a hot fix for Parity, version 1.3.5, but if you're not familiar with the command line (like me) then you might have a problem installing it.
If you type brew install parity then this will install the latest stable version of Parity, which at the time of writing this is version 1.2.4. With the help of the great community in the Parity Gitter channel, I was able to install 1.3.5 and get everything syncing again using the following steps.
Updating Homebrew
Open a Terminal window
Type
brew updateType
brew upgrade
Updating Parity
Open a Terminal window
Type
brew remove parityto remove your existing installation of Parity.Type
brew install parity --betato install the latest beta version of Parity.Type
parity --gethto start syncing.
Troubleshooting
[Error message] Database migration unexpectedly failed
If you type parity --geth you might get the message Migrating database from version 6 to 9, followed by a progress bar and then another message, Database migration unexpectedly failed.
When this happened, I uninstalled parity and started again with the command brew remove parity. Make sure you have plenty of disk space, which people say could be a cause of the error message. After reinstalling with brew install parity --beta you should now be able to type parity --geth without the error message.