The Backbone of South America and a Model of American Spanish
Andean Spanish is often considered the "purest" and best spoken Spanish in the Western Hemisphere. Perhaps, if the Mexicans did not use so much native vocabulary, they would have won the title. Even if it is true that Andean Spanish is the closest to Castilian (the Royal Academy's linguistic gold standard), not all the people living in all regions of the countries through which the Andes pass speak "andean" Spanish. The northern coastal areas of Colombia and most of Venezuela fall under the linguistic spell of the Caribbean basin -- and speak antillano Spanish. The western coastal areas of Colombia have a larger population of Africans who have their particular dialect of Spanish known as chocoano. In fact, with regard to dialects, the Spanish of Colombia is as varied as her landscape.
The same may be said of Venezuela and Ecuador, although somewhat less so. The areas of all three of these countries that border on Brazil do so in the Amazon basin, where the Spanish also takes on some peculiar regional features, one of which is a sing-song quality.
Above the coasts, but not in the highest elevations, one finds many centers of government, universities, convents and monasteries -- in other words, places that have influenced the histories and overseen the education and cultural life of the ruling classes -- who always looked to Spain for their models. These institutions have wielded a conservative power over linguistic change -- that is, they maintained standards by modeling them. Power is linked to language -- speak like the ruling class and you just might be heard.
The Andean nations -- those with a lot of territory in the Andes are Colombia (a tiny bit of Venezuela can fall in that category), Ecuador, Peru, Chile and Bolivia. Spanish in the Andean regions of these countries tends to be clear, well articulated and easy to understand. There are differences among them to be sure -- Ecuadorans tend to speak with a slight clipping pace. By comparison, because they tend to speak a bit more slowly than the Ecuadorans, Peruvians seem almost circumspect when they speak, almost as if they are deliberating within themselves. The Chileans are, as a group, almost in a class by themselves. While one characteristic of Andean Spanish is clarity, the Chileans often mumble and chew the last parts of words or let their sentences trail off -- much like speakers of American English.
Bolivians tend to speak clearly as well, although often with a bit of a sing-song quality that tends to make their words seem as if they are drifting out of their mouths.
In all, educated speakers from all these countries will tend to sound more like each other than say, an uneducated speaker and an educated one from the same country.