In terms of ease of learning, extralinguistic factors are generally more indicative. For example, availability of intensive courses, quality of those courses, a

In terms of ease of learning, extralinguistic factors are generally more indicative. For example, availability of intensive courses, quality of those courses, availability of materials/cultural output, willingness of speakers to interact with learners (either for reasons of inability of communication otherwise or for reasons of ideology), similarity of culture or cultural concepts between the learner's culture and the one of the language they are learning. All of these have as much or more impact on ease of learning than any index of grammatical complexity. (Edit: Basque has excellent courses run through AEK and Basque speakers are usually very motivated to talk Basque, so if you want to learn a language I would highly recommend it, oh and there is a mass of culture like music and films).