English is one of my six languages. [pashto (native), Urdu/Hindi, Farsi, Spanish, and Arabic]
But I find it much easier to think in English. The transition was a little hard from Pashto but I seem to be able to safely switch between the two. [I can't think in the other ones since i haven't mastered them...yet] Although it depends a lot on the environment and audience.
Reasons why I find English to be easier to think in than all the other languages I know:
1. Clarity. The vocabulary in English greatly affects my ability to articulate thoughts without using unclear words.
2. Greater understanding through synonyms. My first points segues into this point quite nicely. At first, when I tried to learn English the grammar, syntax, and vocabulary all appeared to be a conglomerate of boondoggles. (See what I did there?) They seemed stupid and bland. But with greater mastery came better articulation. It took a while but once you get the hang of it, you can choose and manipulate words willfully. My friends dad says, “you've truly mastered a language when you can make puns in it”
3. Distinct ideas through words without the unnecessary details. When I started using the language more frequently, I noticed the absence of gender, plurality, and the presence of passive voice. In comparison, Pashto, Arabic, Spanish, and the Hindi/Urdu languages have huge restrictions on word forms for specific genders. In my opinion, this greatly inhibits a person from voicing his thoughts clearly by preoccupying the brain with useless gender assigning. and it takes away more than the amount of information it adds. You can certainly disagree with this depending on what you deem as valuable information to be put in a sentence.
4. Flexibility. You might have traced my train of thought by now. With the freedom that words have in being able to attach to one and only one meaning [there are exceptions of course] it adds great flexibility in articulation and instead of imposing restrictions, it opens words up to be manipulated in more beneficial ways. The possibility of adding suffixes and prefixes is a great thing that English has.
5. The amount of work that has been done in English. My fifth point has more to do with the fact that the English world has made much progress while the other languages I know haven't. They are simply not on par. This in turn has greatly simplified the language and has made it more useable.

Still have a question Ask your own!