Plant-based protein powder

If you mean plant-based protein or nutrition powders, the strongest flavors for covering earthy/green/legume notes are generally rich, roasted, or warm dessert flavors, rather than bright fruit flavors.

Best flavor choices

There is actual sensory research behind this. Pea protein commonly produces hay, tea, green, bitter and vegetal notes, and research into masking specifically found that “brown” flavors such as caramel are particularly effective.academic.oup.com

Chocolate and mocha are especially reliable because their roasted/bitter character overlaps with and distracts from the vegetal character. A current flavor-formulation guide likewise ranks dark chocolate and coffee/mocha very highly, while finding berry and citrus considerably less effective.academic.oup.com+2

If you want sweet + minimal earthy taste

I'd rank these:

1. 🥇 Salted caramel — rich sweetness plus caramel's strong masking effect.
2. 🥈 Chocolate caramel — probably the safest dessert-style combination.
3. 🥉 Vanilla cinnamon/chai — sweeter and lighter, while the spices help hide the base.
4. Mocha — excellent masking, but less conventionally sweet.
5. Vanilla — pleasant, but formulation matters a lot. Research specifically found that vanilla designed for plant protein can mask pea notes much better than ordinary whey-oriented vanilla.www.synergytaste.com

One interesting caveat: simply making a plant protein sweeter doesn't necessarily solve the problem. Flavor and sweetener need to work together to suppress the underlying bitterness/earthiness; otherwise you can end up with a very sweet powder that still tastes vegetal.www.glanbianutrition.com

If you're choosing a flavor for a specific supplement (pea protein, hemp protein, greens powder, collagen alternative, etc.), tell me which one—the best masking flavor changes substantially with the underlying ingredient.