taking acid in large amounts is harmful. doing it repeatedly is harmful. acid can react to people's bodies in very negative ways, so it's generally good to NEVER do it by yourself, especially if it's your first time
weed is not harmful if done in moderation/not every day, however there's a number of studies that observe it having negative effects if done regularly.
tl;dr acid is def more harmful than weed. don't do acid alone. bring snacks if you smoke
source: studies and smoking fat doinks