Native read/write support since 10.6, just needs enabling.
First, uninstall NTFS-3G, Paragon or whatever else if you're using an app.
Then
1. In Terminal, type diskutil info /Volumes/volume_name, where volume_name is the name of the NTFS volume. From the output, copy the Volume UUID value to the clipboard.
2. Back up /etc/fstab if you have it; it shouldn't be there in a default install.
3. Type sudo nano /etc/fstab.
4. In the editor, type UUID=, then paste the UUID number you copied from the clipboard. Type a Space, then type none ntfs rw. The final line should look like this: UUID=123-456-789 none ntfs rw, where 123-456-789 is the UUID you copied in the first step.
5. Repeat the above steps for any other NTFS drives/partitions you have.
6. Save the file and quit nano (Control-X, Y, Enter), then restart your system.
After rebooting, NTFS partitions should natively have read and write support. This works with both 32- and 64-bit kernels.