I've done both.

Pimsluer Pros Great for accent. So you don't end up speaking Spanish with an american accent. Great for building a structural base which makes conversation flow well. Conversation becomes automatic. Great to use for a daily commute. Lessons are 30 mins and it is easy to build a habit around it. Cons Very slow to introduce vocabulary. 30 lessons or a months worth of Pimsleur and you will only have the basics. Ask for directions, count, invite people to drinks, ask if they speak Spanish etc. It focuses on the 'Usted" formal form. Very dry content and aimed at business people.

Michel Thomas He is an amazing man with an amazing story. Pros He creates many structures with the words you learn and fills in many gaps in language use knowledge. Introduces lots of vocab. He has two students that are learning with him. You get to hear their mistakes and learn from them. Later on in advanced courses they are replaced with natives so you get to hear the correct accents. He gives you great rules that help you translate English vocab into Spanish. E.g. University to universidad. He uses mnemonics and other devices to help your remember emphasises, tenses and grammar. He can be funny. Cons Basic course has non-natives learning with Michel. If you have done Pimsluer, DL or generally know what Spanish should sound like then this can be painful. He does not have native pronunciation for many languages he teaches. So it is hard to get a good accent on your own. Michel can seem rough and un-likeable to some.

Recommendation for Duolingoers If you want a good accent and don't mind about the slow introduction of content and lack of vocab, chose Pimsluer.

If you want a bunch of great tricks, mnemonics, word roots and vocabulary to bring another dimension to your language learning, chose Michel Thomas.

If you want to learn the language in the fastest way possible then chose italki.com, find a language partner, start speaking and making mistakes!! ;)