There are multiple things to consider when gifting...
Loved gifts give 80 friendship for an average quality item.
Liked gifts give 45 friendship for average quality.
Neutral gifts give 20 friendship for average quality.
Dislike gifts lose you 20 friendship for average quality.
Hated gifts lose you 45 friendship for average quality.
Then there is the quality. Silver quality adds 10%, gold quality adds 25% and iridium adds 50%... but ONLY if the gift is liked or loved. Giving someone a high-quality item that they hate isn't going to lose you more friendship than one of average quality, for example.
So, if we look at an average quality loved gift's 80 points and compare to the best of the best you can get for a liked gift... well, 45x1.5 is only 67.5. If you can manage to get a loved gift for someone, that will always be the best gift you can give. If you can find a loved gift that has a quality, you're even better. You can do better than 1 heart per week if you can manage to get loved gifts for someone that are iridium quality. 2 iridium quality loved gifts is 2x1.5x80 + 10 = 250 friendship points which is 1 heart right there. Presumably you'll also talk to the person.
Also, gifts on someone's birthday? They're worth 8x the friendship points... and this applies to hated, disliked and neutral gifts too. You'll also be asked to give a gift to someone at one of the festivals, and that gift is worth 5x the friendship points. You want to make absolutely sure you're giving people something they like or love on their birthday or at that festival. The math for that, though? An iridium quality loved gift on a birthday? 80x1.5x8 = 960 friendship points. That's almost 4 hearts right there... and if you give a hated gift, that's -45x8= -360 friendship points... that's almost 1.5 hearts. You don't wanna do that.