I think all three are equally strong. However, I always needed to review their grammars, spelling rules, etc. to avoid mixing them up. Practice was definitely key in achieving and maintaining native fluency.
For me, that especially counts for German and English, for which I needed a constant reminder on stress particularly. You know because in English, we often infer meaning by stressing syllables, such as in content (noun) and content (adjective), but German stress is often represented by writing the letter twice, such as in “Mutter” and “besser”.
So, when I was younger, I used to write English words with double letters to show the stress I heard when pronouncing them, like “musstard” and “bitt” and “quitt”
Thankfully not anymore…
Also German things are not all gender-neutral syntactically like in English. And Arabic does not have any grammatically neutral gender at all. So, I often had issues guessing whether things in German are masculine, feminine, or neutral and often miswrote determiners as a result.
What about you? Any challenges you have faced with the languages you know?