"requiring less heals from a healer"

With more HP you can withtstand more damage, so less need to heal.
With more mitigation you can withstand more damage too, so less need to heal.

When it comes to helping the healer, any of the two options work. Personally, when solo healing a tank, I prefer a full vit one that knows how to use cooldowns than a full str one that knows how to use cooldowns too.