Too many factors go into what makes a language easy or hard for any given person. There simply isn't an objectively easiest or hardest language.
As a native English speaker: I studied French for 8 years, up to the first year of my uni course. I dropped it in favour of Russian which I had at that point been learning for a year and had actually failed one of my first year modules and was having to retake it.
However, Russian from the start made much, much more sense to me, and I knew that it would be harder to actually improve my French (having just spent a year getting more and more confused) than it would be to get up to speed with Russian.
I went on to get a 2-1 in Russian, despite struggling with illness throughout my uni career. Clearly, a good move!
For me, Russian made a hundred times more sense than French, and it was therefore "easier" for me, despite the different alphabet, despite never having used cases before, despite aspect (yikes) and verbs of motion (double yikes), despite that I had been learning French for seven years before I had ever even seen a word written in the language.
English tends to be easy to get by in/be understood, it's not especially easy to be truly fluent and nuanced, and we also have an enormous vocabulary. I've met dozens of people from all over the world who would say they speak English, and I can think of literally only one whose English was really as fluent and correct as she thought it was!
When I learned Croatian, that was coming off a year being in Russia, so it seemed very easy to me. Arabic I found incredibly difficult to teach myself even a little: Hebrew I've made quite a bit of progress, although they're very closely related languages.
Even with constructed languages, a person's mother tongue will influence how easy or hard they find it. I'm finding Esperanto fairly user friendly, but then, it's written in a script I've been using for thirty years, its vocab and grammar are drawn largely from languages I've studied to some degree, and I'm comparing it directly to my other most recent attempt, Hebrew! Given the circumstances, it's not surprising I'd peg it as being relatively easy.
Languages which came most naturally to me? Russian, Croatian, Esperanto. But those are very specific to me, I don't think those languages are easy per se, that others would have the same experience, or even that it's possible to judge any given language as objectively easier or harder than other.
Fluent: English, rusty Русский
Learning: עברית, Esperanto
Previously learned/would like to brush up: Hrvatski
Bits and pieces of various other languages!