Wiz lvl 6 or giant lvl 7?

For me it would be wizards because they would be in high demand in my clan for wars, but I'd probably do batching troops before that. Jmho though.

Depends on your composition.

If you do raids like me w/ giants, archers and wiz then giants get my vote since, they comprise majority of the army.

It depends on which you use more frequently. I personally would pick Wizards first even though the stats boost aren't that high.