I drive an 08 sonata 4-banger and had an 01 SSEi for 2 years. I can tell you that the SSEi would be the choice. I can only get about 22-25 mpg around a spread-out town and I drive from Auburn AL to Mobile AL on a regular basis can can never get past 28mpg. The Hyundai'* 4-banger can't drop down the RPMs when doing 80 like a 3800 engine can. In my Bonnie I got 33-35 on the same trip. I think it is also because bonnevilles are very aerodynamic.
Don't get me wrong, I like my Hyundai, and if you wan't a kick *** warranty (10/100) then get one. It'* the smoothest 4-cyl I've ever driven. Shifts almost as smoothly as a 3800 and you can't tell it'* idling with the radio on. These emissions standards new cars have to abide by really kill gas mileage. Bonnevilles were built a while ago so they are less restricted so they can muster more mileage than their new-age counter parts.
Another thing about a bonneville is the features. HUD, memory seats, air compressor built into the trunk, Homelink, nice sterios (the Bose system anyway...). Lots of features that you won't find on a Hyndai unless you get the Genesis...
Charlotte-'01 SSEi loaded. Sold at 41k. I'll miss you ole' girl.
Sandra-'08 Sonata GLS. Silverstar Ultra bulbs.