I've been pretty happy with SmugMug...it isn't cheap if you need lots of space, but it does offer some nice options and if you pay for the "Pro" level, you can offer pix for sale at your own prices. That is one of the reasons I set it up and pay the money...It is also pretty straight forward and allows you to set a variety of categories and sub-categories to organize your photos. It seems pretty easy for the people to wander the site and find pix they might be interested in looking at or purchasing. Easy for them to purchase too. You can go back and reset prices and available purchase items or add things to galleries at any time.
Shutterfly is OK...it can be a bit confusing at first but it makes sense I guess. In SmugMug, if you click on a gallery, you go to a page (or set of pages) with all those photos. In Shutterfly, you can add albums that really aren't displayed unless you set up a page or part of a page to display that album. I can't say they are the best quality prints, but I do like the options they offer (like the calendar and photo books) that are available for purchase. Setting up and ordering those is pretty easy and they're quick with delivery, all reasonably priced and LOTS of options.