If you traveling round trip, why not take Acela one way and NE Regional the other?
I have ridden both. The higher speed of the Acela also results in more side to side car rocking motion over the portions of track that are not in the best condition (e.g. in my experience Providence RI to Boston MA, several years ago). If you like to get up and walk through the train you may prefer the NE Regional. The extra fare for a business class car on the NE Regional is worth it, more legroom and quieter passengers...