Interception or Protection?

Interception is considerably better but...

The general rule of thumb is Interception will outperform Protection at low levels (especially before level 4) and Protection will be better at later levels... At high levels neither are remarkably strong. Enemies get more attacks as they level, you keep the same number of reactions -- 1.

(I don't think the general rule is correct.. Attack damage in 5e scales through multiple attacks in most cases, not higher damaging attacks. Higher CR monsters that hit incredibly hard also hit often, it's rare to see one attack that does 50+ damage, but common to see three attacks that do 20/15/15)

There's a hint in the description of the two fighting styles. Interception doesn't require a shield, Protection does. You should intercept low-AC allies and you should Protect high-AC allies. Why? If a creature has a high chance to hit the target, forcing them to roll again doesn't reduce the odds of the attack missing.

A better rule is to think about who you are trying to protect? Interception works better with squishy allies, Protection works better with tanky allies.

https://www.dndbeyond.com/forums/dungeons-dragons-discussion/tips-tactics/121049-interception-vs-protection

https://rpg.stackexchange.com/questions/190408/is-it-unbalanced-to-allow-the-protection-fighting-style-to-modify-an-attack-roll

Interception does not require a shield, Protection does.

These features do slightly different things. Advantage and disadvantage do weird things to the math in the game but they are effectively +/- 5 on the roll. Disadvantage is good when the creature isn't expected to hit the target (has high AC), if the target has low AC or the attacking creature has a high chance to hit, disadvantage isn't going to do much.

The other thing to think about is to think about how much the damage reduction matters. If you're intercepting a target that has 30 health and the creature attacking it expects to do 10 damage per attack, this means the target can effectively take 4 hits instead of three.

The effects of Interception have the potential to cascade into future rounds in a slightly different way than Protection does, especially when combined with healing.

Interception gets applied when you know the target will take damage. Protection is a bit of a gamble since disadvantage might mean they would have missed anyways or they would have hit anyways. This isn't a good way to look at it because the odds of these events happening determine if it was a good idea not the results.