Can't go wrong with any of those choices but there are differences between them. Unless you're very much into seafood and only seafood you could eliminate Street and Company. If all you want Is seafood, move it up a notch.
555 can be great and inventive. It's only real drawback is its location in the Arts District vs the Old Port where most of the action is if you like walking around before/after dinner.
Hugo's has been talked about a lot. It can easily be the most expensive but when it's on it really is in a league of its own. Potentially the greatest reward but that comes with the greatest risk factor as well. Nothing worse than dropping 4 bills and not having been blown away.
Bresca is small. As in very small. Intimate. The menu is small as well. Small enough that a picky eater can be in real trouble. The food is great but the deserts are in a class of their own. If you're into the quiet, small and intimate scene Bresca is a good choice.
Then there's Fore Street. Very lively. The best ingredients cooked simply yet refined. Fore Street is really the place that put Portland in its place on the culinary map but it does not rest on its laurels. It manages to stay fresh and for me it's the closest thing to a sure bet in the top tier of Portland restaurants.
When I have trouble choosing, I often don't. Do app's at Eventide Oyster Co (owned by Hugos - they share a kitchen) and then take that one block walk to Fore Street.
Don't know if I helped or made it more difficult for you.