Uggla,
From Wikipedia:
"A master boot record (MBR), or partition sector, is the 512-byte boot sector that is the first sector ("LBA Sector 0") of a partitioned data storage device ..."
I've always been confused as to which is better, but I do know that during install, you are asked if you want to install Grub to MBR or you can chose a partition (sda or hda, etc.).
putz