Since the last bus travel thread on this forum, I've become intimately familiar with ground based travel in the NE. I've tried all the NYC-BOS bus lines except limoliner and while YMMV, I have found the following:

For comfort it's AMTRAK all the way. Wider seats, more legroom, plug ins, the ability to get up and wander to the cafe car, etc, etc. This is also often the most expensive option with fast Acela trains (3.5hrs) costing $130+ and slower regionals (4-4.5hrs, no wifi) at $65+

Megabus has more destinations and often cheaper fares that the others. I find the double decker buses have an even greater cattle car feeling than the single level. The wifi is hit or miss, but if your mobile has tethering/ mobile hot spot, that's not an issue. The absolute worst thing about Megabus is the absurd (and previously mentioned) chaos in their NYC boarding area. I now avoid them just for that reason.

I've taken Fung Wah and Lucky Star once each. While both buses were older, I certainly didn't feel unsafe. That being said, the same day I took Lucky Star, they had a fatal crash on one of their other routes. The Chinatown boarding areas for these two are more convenient for many than the Penn station/ PABT areas the other lines use.

Peter Pan is a Greyhound operation from PABT. They have frequent departures and consistent, if slightly higher fares. Most of their coaches have wifi and some have plug ins. For those coming or going further north than BOS, they have combined offers with Concord Coach (Bangor, ME-NYC $99r/t and you can break it up if you like)

My favorite so far is Bolt. Also owned by the Dawg, this is a different animal altogether. More legroom than Megabus, reasonable fares, comfortable leather seating with plug-ins, much calmer curbside boarding (perhaps owing to fewer destinations?). My last NYC-BOS trip on Bolt arrived 30 mins EARLY!

I have flown PWM-LGA a couple times and honestly, I should've taken the bus. Both times, I arrived in Manhattan a full hour later than If I had stayed on the ground.