This is a link directly to the current client; the client at this link will be the most updated client available.
If you have any problems with the client or java please refer to the links below.
Download Client Launcher: Click here
If you're having trouble starting the client, you should try updating / re-installing the latest Java version.
If your computer doesn't recognize .jar files, you need to set it to open with javaw.exe.
There are guides and downloads to help you troubleshoot below.