Thailand produces some of the world's most complex and aromatic food. The question of street food versus restaurant isn't about quality — it's about what you want from the experience.
Street food is best for single-dish mastery. The pad kra pao vendor who has made nothing but basil stir-fry for twenty years has a level of technique and wrist speed that most restaurant kitchens can't match. When a vendor cooks one dish, they cook it extremely well. Find them by looking for the longest queue of office workers at 12:15pm.
Restaurants — particularly those in night markets — are better for groups, variety, and dishes that require longer prep time. A proper massaman curry takes hours to develop its layers. A tom kha gai needs time to infuse. These dishes are better ordered from a kitchen that has time to make them properly rather than at a street cart serving 200 customers an hour.
The northern food of Chiang Mai (khao soi, sai ua sausage, larb) is best experienced at sit-down restaurants where the recipes are more regional and the fermented ingredients need careful sourcing. Southern Thai food, dominated by fresh seafood and intense curry pastes, shines at both formats depending on proximity to the coast.
Budget-wise, street food runs 40–80 baht per dish. Restaurants charge 120–250 baht. Neither is expensive by global standards, and both can be exceptional.