I think its very difficult to answer. There is no guarantee of happiness in either and it really depends upon lots of factors, your child's personality, their needs, the teachers, the classmates and the school itself. What I do know is if it isn't working you can change things.
My son is almost 4 with a high functioning ASD profile. We are abroad and in the last 12 months he has moved from creche to a montessori preschool, to a small English preschool and now finally an International preschool. What we learned is that the montessori school was the wrong setting with zero pastoral support and in the space of 4 months DS became miserable, withdrawn and a school refuser. Why? Because he is was overwhelmed in a big class, not enough supervision, a couple of bullies, his native language was not widely spoken, the set up was too rigid, no toys, school only wanted NT kids etc. We moved him to the small English preschool & saw him immediately change, he was happy again, thriving. Why? Because he was in class with 2 teachers and more often than not less than 10 kids, a personalised approach - weekly teaching themes related to child's interests, passionate teachers (privately owned business), lovely classmates and parents, visibly learning something new every day. It was incredible. Unfortunately they only provide teaching for kids at preschool age so we had to move him to the international school where he is now and which he loves. Honestly, its a mixed bag. We moved him there because they welcome SEN students & have onsite psychologists, occupational therapists and all the pastoral support. I instantly knew when i wemt to visit it that he would be happy there - amazing playground, big classrooms, lovely teachers, amazing facilities and huge array of extracurricular support, forest area etc - focus on outdoor play. On the one hand I have a huge sense of relief knowing my DS is happy, not refusing school, accessing mainstream education without any intervention at present, making friends and I would pay for it no matter what it costs. But we felt we had no choice but to send our son here because of his ASD diagnosis and knowing that state schools here do not have adequate SEN provision and our DS would not cope well in an environment not in his native language. I don't love his current school, i'm not convinced on it long term but I know its the best place for my son right now.
My advice is - you know your child best, visit the school get a feel for it, what environment does your child need to thrive. And if it doesn't work out, you can always change things.