Currently only Hand of Glory is overwritten once Blessing is cast but not the other way around.
Reason i am asking on my Paladin and Cleric i prefer to have Hand line due its stacking with there self buffs while on my other classes i play it don't really matter.
Its just frustrating that if you think that you fully buffed and than the rest of the raid is getting buffed that you will need to declick Blessing + Symbol and Recast Hand + Selfbuffs.
Cleric Selfbuff: Armor of the Pious http://www.thehiddenforest.org/webtools/spells.php?id=5276
Paladin Selfbuff: Armor of the Orc Slayer
http://www.thehiddenforest.org/webtools/spells.php?id=8924
Cleric + Druid buff links so Tyler just need to click

Hand of Glory http://www.thehiddenforest.org/webtools/spells.php?id=8996
Blessing of Steeloak http://www.thehiddenforest.org/webtools/spells.php?id=5366