Hands down, "Raw Disks" is direct access to the physical disk and by far the fastest access and disk I/O. The downside is you cannot move the VM to another machine without imaging the raw disk.
But, you asked which is the fastest "Virtual Disk". Raw Disks are not virtual disks.
And no, you cannot switch between virtual and raw types (unless I am missing an upgrade or something).
As for which virtual disk is faster? Fixed size is much faster than that dynamic type, which expands. Fixed disk is no where near as fast as Raw, but still much faster than dynamic.
Now, if you are asking if it makes a different to break the files into chunks or have one single large file - there are many discussions on the net that go both ways. Personally, having them split up into multiples I feel increases your host OS' seek time as it must go and find all different files, especially if you defragged your local drive.