would you go for united or american gift cards?
delta allow only 3 per reservation so less useful
american allows 8 per reservation so can end up being a nice amount.
united let you add it all to the registry but the registry will expire after 5 years without activity (yes its a long time and yes easy to add more to) and in theory if they ever got annoying would be harder to sell.
problem is with the BP at 2cpp i find it hard to justify using gift cards and therefore would likely end up selling them off