I can't comment on the 348 specifically but I can on the Vista series as I've owned a 248 and now a 288. The Vista is one of the best space users out there, especially on the smaller end. The size ou are looking at the difference between the variious manufactures in how they use space, IMHO, narrows.
As to overall quality, I see very little difference between the Four Winns brand and the Sea Ray brand. I think you will fond the fit and finnish very comparable.
As to the Sea Ray, you are correct, you will be limited to Mercruiser power as Brunswick owns both Merc and Sea Ray. It seems these days you are mostly limited to MarineMax as your dealer since they have all but sewn up the Sea Ray brand. I've heard good and bad things about MarineMax. I have a friend who has been in a fight with them over his Sea Ray 260. They serviced his boat and replaced the exhaust manifold gaskest and installed them incorrectly. He had major water intrusion and his engine is toast. Even though they admitted their mechanic screwed up they will not fix his boat, (except for him paying $5000 for a rebuilt). His attorney advised him to just repower as the cost of fighting them ( which looking at the documentation he has said they would win) would be about the same. I can tell you this has been going on since January and he will never buy or deal with MarineMax again. Sea Ray would not go up aagisnt MarineMax and help out, hence Sea Ray is permanently off his list as well.
Four Winns factory service has been excellent for me as has Volvo. Volvo replaced and engine for me because if a faulty oil line. They had the engine shipped and even called my dealer to arrange the service call and get it scheduled ASAP. As to Four Winns, the tank monitor system has been fixed a couple of times, called them and told them I was unhappy with the unit that was installed. They paid for the unit of my chaoice and paid the dealer to install it.
As to the SmartCraft system. It is propritary to Mercruiser. The new common standard is NMEA2000 which used a common bus to share info. Volvo has the EVC module that will provide info to the NMEA2000 network. I'll be getting some info on this for my boat hopefully this week. Belolw is a pic of the install I did in my boat. You can find more info at these sites
LowranceNet,
Power and Motor Yacht Article,
Tank Filler with Display,
Bennett Trim Tab Indicators
Add a tee and you are installed and the info is available to any of the displays.
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Jvalich
http://www.badcock.com'04 FW 288 Vista "Mental Floss"