Having take a bus and amtrack I'll take amtrak. My bus was just as late, and there was less opportunity to walk around. Amtrak has sleeper cars which are probably better than the coach seats I was in (the bedrooms areea good price for 4 people but had 5 and so couldn't make the numbers work)
A trick that won’t always work - get the sleeper for four and have the fifth visit. You just gotta be nice to the conductor and the sleeper attendant.
But the other option is to just all get lower level coach seats next to each other - sometimes five or six is about all they have down there. Make a new friend!
I've taken a "luxury" bus from the Boston area to NY once. I'll stick to Amtrak although, given where I live, it's not very efficient. Boston area to DC really takes too long though I've done it.
I hate driving into NYC though I've done it with someone else (or because I was headed somewhere else afterwards). As you say, with multiple people, the numbers don't really pencil out--especially given it takes longer for me.
It makes me so mad that we have a rail system that has all the structural necessities to make HSR a reality, yet we're stuck with service that last looked modern 50 years ago. If there's one place in the USA that would have the ridership to support a HSR it would be the Boston-DC metro axis.
I took Amtrak from Boston South Station to Montpelier. You have to go south to Connecticut before you can get the Vermonter. The Vermonter was canceled due to contention with a disabled Metro North (or something...) and my connecting train turned into a bus.
When I've gone to NYC, it's honestly been less hassle to just take the bus.