any advantage to a 5.2 over a 5.9 ?

Just wondered if there is any reason to do a 5.2 rather than a 5.9

Obviously the 5.9 will have more power, but will the 5.2 get better mileage.

Will a 5.2 be a major improvement over my old 318 ? Old engine is low compression due to 360 heads.

Seems to be more 5.2's available around here for a decent price.
Guys selling 5.9's are wanting $750 to $1000 for one with mileage from 100k to 181k.

Or would you figure, if your doing the swap might as well go for the bigger engine?