Rot Me
It's slower but cheaper to take the Rot Me to Mae Sai. This bus is non-aircon, instead there's a fan (phatlawm) from the ceiling. Expect your fellow passengers to bring all manners of things from live chickens, large bags of rice etc. This bus is slow because it stops and picks up anywhere on the Phaholyotin Road to Mae Sai. But I think it's not more interesting one I'd take - just for old time's sake, a trip down mrmory-lane, and for the people-watching opportunities. Fare is in the low 30s - depends where you want to go.
See the fans
Bags are stored in the first class section
The way to busses work is they wait from them to fill up (tem) and then they go. There's also a schedule that nobody really sticks with. When the bus driver thinks it's full, he'll leave. Some seats appear empty but are held in reserved for passengers who called and are awaiting at some ban nok en route so don't lile down thinking it's you're lucky day you've gotten 2 free seats abreast.
The driver also places a placard on the windshield to denote if bus is full or has space. Green card says "wang". Red card says "Tem". So the flaggers will know what they're chances are.
I like this bus. I would take it if I were alone. Slower but more atmospheric. The full experience.