Do you have friends on your legacy server or on a non-legacy server?
If so, start there.
Do you have any special items that you cannot get otherwise (like Sprint Shoes or whatever the bonus item was for FFXI link)?
If this is important, keep your legacy.
Do you have more than one crafting/gathering classes over level 10.
It might be worthwhile for you to keep your legacy rather than re-level-up those abilities.
Is it important for you to be able to find player made gear at all levels at launch?
If so, consider legacy. New servers will have a shortage of HQ gear until the market begins to stabilize and populate with crafters.
Do you want to be involved in the economy and attempt to control/profit off of certain areas of the grind?
Consider playing on a new server.
WoW Blackhand-US-Date of Retirement: 9/21/2010... /Sigh
Devari - 90 Rogue 85 DK Druid/Mage/Warrior 70+
FFXI - Shiva "Retired.... Or not? One more try, honest."
Desmar - 65 Sam 36 Mnk 18 Thf 12 War
FFXIV - Devari Garamond - Sargatanas 50 Paladin / Culinarian / Weaver / Armorer
Beta - Devaria Ariadne - Ultros - Pugilist