Want a 2005 Altima... V6 or 4Cyl?

I am looking to purchase an Altima for no more than 18 grand... I want somethign with under 30K miles on it with a sunroof and rims... Cheap gas would be nice too... How are the V6's on gas in the real world? I know the EPA claims 20/30 for the V6, and 23/29 for the 4cyl.. Why the 4cyl isn't as good on the highway is beyond me, but maybe its because of the extra gear in the trans? Or maybe this isn't a real world number... either way, what would you recommend? Does the V6 require premium fuel? And how did these cars rate in the rash test WITH side airbags? I know they did poorly w/out, then again so did every other mid size of the year... maybe the rating wasn't too real world oreinted either...?

picked up the 2007 with the v6 3.5, 6speed manual.... in on the hwy long distance, no ac running about 80mph for 300miles.. i get 33/34 mph with ac 31.4..., oh and with ac and running about 95 for 250miles 28-29
city/hwy stop go, go fast, go faster, go even faster.. about 24mpg..

i do not like 4 cyc not enough power.. gas milage, i have no idea on your year.. basically, it is just an average, but depends on your foot. also the 4 banger has to work harder to push same weight with greater resistance. ( higher speeds ) thus fuel consumption can decrease..