The 2015 Lexus RX 450h is the top choice in the lineup, of course, if you're shopping for a green family-sized wagon. With its well-coordinated powertrain and a price that's only modestly higher than the RX 350, the RX 400h might make good fiscal sense, too.
EPA ratings place the RX 450h at up to 32 mpg city, 28 highway; but the last time we drove an RX 450h, over mixed driving conditions, we didn't see anything close to that EPA rating—about 23 mpg overall, with all-wheel-drive model (rated 30/28).
As for the normal gasoline RX 350 models, they're a little more consistent with other mid-size crossovers in the segment. Keep in mind that it does only have two rows of seating, for a total of five, at a time when many vehicles around its size are offering a third row. But with true comfort for four adults and cargo, we don't see its mid-20s highway numbers as all that bad, comparatively.
RX 350 models now all include an 'eco driving' light that simply tells you when you're driving gently (and efficiently).