I say you can't go wrong with either for a nice ride, but I would lean strongly torward the Camry. Toyotas haven't kept their squeaky-clean reliability like they had a couple decades ago, and Buick has improved from what they were, but they are far from equals.
An 07 Camry will feel like it is epoxied together. Stiffer unibody, better assembly, higher quality interior materials. The materials used to make it will last longer by far. Take a look at the same cars with higher mileage and look at the rotting, torn leather in the Buick and the chrome tape peeling off the dash trim. Around the time GM was getting a little better at interior assembly, they started using really pathetic materials from the absolute lowest bidder.
Both engines will run well. The Buick (in terms of repair) will undoubtedly have more failures. Aside from a potential lower reliability rating of the engine itself, it will likely outlast the car. You will almost certainly have electrical gremlins; power seats that like to move when they want to, radios that have quirks, etc. That list is quite long actually.
Just for the sake of comparison, the Camry was a C&D top ten, and has made Consumer Reports best used cars list every year since. All of Buick Enclave, LaCrosse, Lucerne, and Regal made Consumer Reports "used cars to avoid" list. Granted, those are not definitive lists, but I find it hard to believe that they are equal cars if one has made the "avoid" list every year since 2008 while the other one made "best" every year since 2008.
One of the problems you'll run into is a hundred people who have owned Buicks and never had a single problem ever (except the head gaskets, dexcool gelling, plugged cats, recall on seat belts and ignition switches, recall on airbags, and windshield leaks) But that's IT. Nothing wrong ever.
Then you'll have a hundred Toyota owners who bought an appliance and it never had a single failure (for real) and it also didn't illicit any emotional response so they don't give it a passionate review.
Here is a neat tidbit for you. In 1994, my Uncle was an Engineer for DuPont working with Toyota on the Camry and Corolla. His job was to engineer a part for Camrys and Corollas that fails. His job was to make it less boring by engineering a weak link. Then ended up with valve cover gaskets and something else like a horn relay. Research showed (at least in Toyota's eyes) that a car that never fails loses interest. Psychologically speaking, (according to the wording of the study and relayed to me by my Uncle) caring for your car is like caring for a crying spouse. A cheap fix for something that failed actually increases customer opinion of the car and makes them more aware of how cheap it is to maintain.
Conversely, a Buick is something about which some people are passionate. Because of that, they tend to overlook its quirks.
Therefore, my somewhat objective opinion; if you want a reliable appliance that holds its value and will not hold your interest, get the Camry. If you are passionate about Buicks, get the Buick.