My diet:
Comparison

Lecithin vs Lecithin

The short answer
They work almost the same. Sunflower lecithin is the better pick if you avoid soy or GMOs; soy lecithin is cheaper and more widely available.
Side by sideLecithin (Soy / Sunflower)Lecithin (Soy / Sunflower)
Safety score88/100 Generally safe88/100 Generally safe
E-numberE322E322
Allergen labelingMust be labeled as soyNot a major allergen ✓ Better
GMO riskUsually from GMO soy unless organicNon-GMO ✓ Better
ExtractionOften uses hexaneOften cold-pressed ✓ Better
PriceLower ✓ BetterHigher
Emulsifying powerExcellentExcellent

Swapping one for the other

Swap 1:1 by weight. Liquid sunflower lecithin is slightly thinner; reduce other liquids a little in chocolate.

Common questions

Is sunflower lecithin healthier?

Not meaningfully. The main differences are allergens and GMO status.