really seems like the 28i is the way to go. You're getting more efficiency modes + 8AT. Also, if u live in warmer climates, you can just get the sdrive, which handles better, weighs less, gets better mpg and is, maybe faster? (minimally though).
Here's the real question... With the styling on this thing and the ride height, it doesn't really even look like an SUV. It looks like an elevated wagon (kind of like the audi allroad). I think I would rather have a proper wagon (read F20 or F31) or a proper SUV (read F25 or current/next gen X5). The only thing attractive about this is the price.
2011 X5 xDrive 35i Premium - 8AT, Cnv, Tch, 3rd Row, Cmfrt
2011 328i 4dr, 6MT - Sprt, Prm, Cmfrt