Remember that all these trains (whether a Regional or an Acela) are reserved trains (for both coach or upgrade). Unlike planes, "reserved" just means you have a seat on the train - not that you have "seat 17" or "seat 39". Seating on Amtrak is any open seat of your choice.

Personally, for the difference in price, I would choice business class on a Regional (if I were paying for it myself).