I'm biased but I'd listen to my lawyer :) All three if set up and managed properly should provide protection of personal assets. You'd have to follow-up with your attorney on why he thinks a trust is best, it may have something to do with being more difficult to "pierce the veil" if an issue arises, but I don't know MA corporation or trust law. It may also just be a less demanding form of protection on your end as far as record keeping requirements, etc. Again, you'd have to ask him.
Do you have someone who handles your taxes to double-check the tax advantages of a trust over an llc or s-corp? Is your lawyer well versed in tax issues? Personally I prefer deferring tax advice to tax professionals and focusing my time on the liability side.
I think you're already on the right track by hiring professionals to do this stuff for you while trying to keep abreast of it yourself. You should follow up with them on why they think x is better than y. They should have an answer for you, and if you don't like it you can always go somewhere else.