I've had tostones and they are very good, but have not yet tried the amarillos. I just got some ripe plantains today so I will have to make them.
The best thing I've ever had with plantains is empanadas de platano, which is a Salvadoran dish. Dear God, they are incredible! They are made of mashed sweet plantains stuffed with a chilled milk custard, then deep-fried and rolled in sugar. I had them for the first time today for dessert after I was already stuffed full of pupusas or I might have made a meal of them alone.