[Maineboater]

O.P. I feel your pain.....we have been searching for a new boat for months and keep coming back to Tiaras and actually have a 3500 Open under contract at the moment. There are large and subtle differences to all of the models both above and below deck. The biggest difference for the year/budget we found was the Express vs. the Open. The express, like Gmahanna said, is geared more towards seating and entertaining above deck with more built in seating in the cockpit area where the Open has more of an "open" cockpit with room for fishing. We went with the Open over the Express even though we don't do much, if any fishing, simply because I liked the look of the Open hull better (it has the gunwale sweep from helm to cockpit which I think gives it a beautiful side profile vs. the Express with has a pretty level gunwale from front to back with steps down leading to the swim platform. The open we chose still has a lot of seating in the cockpit and where its so open, gives us all sorts of options for deck chairs and such. I really wanted a hard top but for the boats in our age/budget there aren't many with them.....we did consider a Sovran because I really like the hard top and fully enclosed helm, but those MOSTLY only come withe the Volvo diesels and the pod drives which ultimately are a lot more maintenance BUT they do offer more cabin room for an aft lounge/berth setup.
The more you look, the more you'll find the differences and it will hopefully become clear which model you are drawn to.
Good luck in your search, from all of the research I've done, you wont' be disappointed with ANY Tiara!