Which is more common in actual use: นอนหลับฝันดี / ฝันดี or ราตรีสวัสดิ์ ?

Many ways to say it depending on the context and who you're talking to. I would say: bye, phom ja non.

ฝันดีนะ

On 1/9/2025 at 4:43 PM, XGM said:

Which is more common in actual use: นอนหลับฝันดี / ฝันดี or ราตรีสวัสดิ์ ?

Only ราตรีสวัสดิ์ is actually goodnight. This is very polite and quite formal just as อรุณสวัสดิ์ is very polite and formal for good morning.

นอนหลับฝันดี  loosely translates as sleep well and sweet dreams.

Usually Thai people will just say จะไปนอนแล้ว which again loosely translates as I am going to sleep now.

ฝันดี is again loosely translates as sweet dreams although it actually says good dreams.