Both schools are large, and “friendly” is subjective.
Responses from those who have attended neither school are worthless. Responses from those who have attended only one will most likely favor the school they attend(ed). I doubt you’ll get any responses from anyone who has attended both though that input would be most insightful. How people feel about Exeter and Choate will run the gamut and will not be relevant to your decision-making process should you need to decide between these two on M10.
For example, our son loved Choate but, if I had been the student, I would have chosen a different school. My opinion on the school I favored was irrelevant even to my own child. 
Do your own research by delving into the website of each school you’re interested in and come back here with specific questions you couldn’t find answers to there. We’re happy to help, but which school any one of us favors is not the place to start.