The Constitution should never be amended to address an issue which is best addressed by the states themselves. Historically, qualifications for marriage are determined by the state which confers the license.
An amendment who be an absolute travesty to state's rights - and civil liberties in general.
I would allow gay marriage. To create another name for it, like a "civil union," is semantic stupidity. You should be able to marry anyone you like, regardless of sexual orientation - with a few notable exceptions like children and immediate family members, because of the relevant policy considerations.