Duolingo is great for beginning a language. Especially with spanish since it is one of the original languages, it has the most developed features.
That makes a lot of sense. See I haven't tried any of the more fringe languages. How much of a differential have you noticed in quality?!
Well I've tried Norwegian a little, and have completed the Esperanto one (both are only a few months old). Here's some differences of Esperanto and German (German is also one of the original oldies). 1) At the top of the page, there is no "Words" or "Immersion" feature for Esperanto. 2) No Fluency Level Badge meter thingy (not that it really matters because it's not really accurate) for Esperanto 3) None of the following optional skills in shop: Idioms, Flirting, Christmas for Esperanto 4) German has a refined and expanded tree I believe. At the very least it has probably twice the amount of lessons as Esperanto. Some things that are also probably true is that German has less bugs, less errors, and more comments per post, but I can't confirm that. You can use the newer languages on Duolingo without much difference.
Wow that's quite the differential. I know the meter is wildly inaccurate, but it makes me feel accomplished. To be real it goes a long way in helping the learner visualize their progress (however tertiary it may actually be)... I never checked the comments much. Sounds like overall they don't provide a lot of insight, but the community is a great way to converse actively in the language. That makes a ton of sense. Hard to do with 2 posters...