IMHO the best free tool to clone whole disk or few partitions is Clonezilla.
PROS
- it's free and open source
- it supports many file systems
- it's reliable - i didn't have any issues with it
- it can clone disk with bad sectors and you can boot it (tested on broken windows disk)
CONS
- it's free and open source - it could be a problem for somebody
- choosing right options could be tricky
In most cases you can use Beginner mode and click next, next... like in windows :P. Ofc you need to choose correct source and destination disk :)
The problem is, when you would like to clone bigger disk to smaller one.
Beginner mode won't allow you to do so. Luckily there is also Expert mode, where you can choose correct flags. Remember, that your data needs to fit in smaller disk, so you won't be able to put full 512 gb disk in 256 gb :).
Besides standard options you should choose: -rescue in case of bad sectors, -icds in case of smaller destination disk, -v for more info.
Screenshot below:
The next best option would be leaving default setting, like on screenshot:
Last step is important - you need to choose -k1 for resizing partition table:
And that's all. After few confirmations the process will start.