It he works in Orange County, Beacon has the bridge to Newburgh and is on the Hudson Line (about 1 1/2 hours to the city) so that would probably be your best choice. Also it is a really cool and artsy town. It is improving there every year. You are only a few minutes away from Fishkill which has a bunch of convenient places (Home Depot, Walmart, Sam’s Club, a gym, CVS, basically every possible fast food place and also a waterpark in the Summer). I’d recommend there too but it is further from the train/bridge and basically the only place to walk around is the small main street, Beacon is much bigger and has more places you can walk to.
Don’t do Cold Spring. It is isolated with no chain stores except Dunkin Donuts, you have to drive at least 15 minutes to do anything. The only grocery store is super overpriced, and so is the pharmacy, they just blatantly take advantage of the convenience of shopping in town. Also you’re going to get less for your money. It’s one of the most expensive towns to live in in the Hudson Valley outside of Westchester, with less to do and smaller houses for higher prices. The locals, many of whom have lived there for generations, are often unfriendly and unwelcoming of outsiders. I can answer literally any question you have about the town since I was born and raised there and absolutely despise it. Garrison is the same thing but even more expensive and barely has a town at all.
I went to school in White Plains (well Purchase is like 5 minutes from there so I would go there every day for years and know the area well) it is a pretty big city, nowhere near as big as NYC of course but it doesn’t really compare to the other suburbs you mentioned. Also the nearby Tappan Zee bridges brings you to Rockland not Orange so he’s gonna have to drive further. But for your convenience it is only like a 30 minute train ride to the city on the Harlem line.
I go up to Kingston rarely but that is a far far commute to the city or even Orange since it is in Ulster county. Easily 2 1/2 hours+ to the city, with the nearest train being in Poughkeepsie which is a 30 minute drive and a bridge away. I wouldn’t recommend that at all with your workplace locations.
I don’t know the other towns well enough to make an informed opinion but I hope that helps.