Idk. Native speakers are biased. I would trust someone who learned BOTH the languages they are comparing as a second language most. Even then they may have different views depending on what languages they already knew prior (eg, portuguese is a lot easier for a spanish speaker than a mandarin speaker)
My dad (who learned English as a second language after his native Spanish, and also learned Portuguese and Latin, don't recall if he knew any others) used to claim English was one of the easiest languages. I don't recall his reasoning but I think it might have been because the rules (other than spelling lol) were simple and forgiving.
Don't get me wrong, the grammar is definitely easy to understand, but IMHO that's just another point for the 'learn early in life, or struggle' opinion. Adults have a much easier time with more complicated grammatical rules (hi, German!) or even rules with lots of exceptions (hello, Russian!). But having to remember how to spell and pronounce every other word is akin to hell for an adult. (I'm already struggling with it while learning Russian.)
Still doesn't hold a candle to Mandarin or Japanese, of course. These guys are just on a level of their own. :)
