Based on personal experience:
Goods (highest-lowest)
=================
Costa Rica*
Argentina (Long flight)
Brazil (No spanish of course)
Lima (Machu Pichu a must!)
Santiago (long flight)
Panama*
Mexico
Dominican Republic (assuming Caribean is ok)
*Spanish is easier to understand in Panama and Costa Rica (pronunciation).
Avoids
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Venezuela
Colombia
If you're looking for a real sleeper of a place to kick back, scuba, snorkel or just chill - Bonaire (sm Island part of Neth Anitlles - no spanish but they speak papimiento - a combo of spanish/dutch/french - wild!)
Edit: Visas to all/most should be doable if you already have your passport - here is a link to
visa requirements.