The verses in Hebrews are actually speaking more about Christ's relationship with angels than ours. The jews wanted proof that Jesus had more authority then the angels, saying that authority would prove His divinity, because only God can command the angels.
Verse 13 is simply saying that Jesus can order any angel at any time to sit at His right hand while He defeats His enemies, and then make them a footstool. It was the custom of the day for the victors of a battle to place their feet on the necks of the fallen enemy. This verse has good information, and does help in understanading the power Jesus has over the angels, but it has nothing to do with angels being personal guardians.
Verse 14 is simply saying that the angels are ministers for Christ, and that He sends them out to minister to His people. Again, this verse is about the authority Christ has over the angels, it is not about us at all.
However, it still does not support the idea of a 'guardian angel'. It never says the angels are assigned to us, it simply says that they minister to us when Jesus sends them.
These two verses are about the authority Jesus has over the angels.....it has nothing to do with them being "guardians"
Again, it is a myth.
John