Hi you all!
I'm new to the site, and I'd like to contribute to this topic.
I think I can speak about my own experience. I'm a native of Spanish, then I learnt English and then French. I don't know exactly why but French was more difficult for me than English, (maybe because I was older when I started?
)
I think the problem with French is not only the verb conjugations, but also concordance in general. For example, I keep forgetting gender in adjectives.
I find English so practical about that!
I don't think the problem is one of similarity. I think if a language is really different to the one you speak, you will pay more attention and it will be easier not to get confused.
I don't know what language is more difficult -I don't know that many languages.
But for sure, English is easy.