You do not need a visa to enter Portugal if you are a U.S. citizen. Turkey requires a tourist visa for American citizens.
The weather in Portugal is moderate all year long. Turkey is a much larger country with climate patterns varying considerably across regions. In general, summers are hot and sunny
Tukey boasts Istanbul and Cappadocia while Portugal has Porto and Lisbon
A cultural bonanza of colonial architecture, magnificent monuments, and delicious food welcome you wherever you go in Portugal or Turkey