Depending on what equipment Amtrak throws onto your Regional, Business seats might be superior to Acela First. Regional Business generally has a 2-2 configuration with footrests (and sometimes calfrests), and seat pitch approaching 50". However, a former "Club" car may be used, giving you giant leather seats in a 2-1 configuration, even more legroom, a great degree of recline, and cupholders between paired seats. These cars have bar none the nicest seats on any Amtrak equipment anywhere. They're most likely to appear on trains with two-digit train numbers, but can crop up anytime. Sometimes regular coach seating will include such cars, making Regional coach nicer than Business!

Acela First does have a 2-1 configuration, but the seats are no wider than the 2-2 configured seats in Acela Business. Seat pitch is probably about 60", and footrests are included. Amtrak is in the process of converting Acela First seats to leather upholstery, but that does not of course make up for the lack of extra width or lack of calfrests.

Where Acela First really shines is the personalized service, meals, booze, and ClubAcela access.

Hope this answers your question!