Mostly depends on what you want to do with the truck...
Some guys run both to get the most tire clearance.
With a suspension lift, you also get some benefits like more wheel travel, better shocks, better handling in the rough stuff, while a body lift keeps everything under the truck in its stock configuration, but allows for larger tires.
Body lifts are generally either 2" or 3" max.
Suspension lifts can go to over 6" and they sort of go in steps...
First spacer blocks and shackles (or a Torsion bar twist and shackles if you have a 2nd gen or later) ) (good for 1-2"), then llonger springs and front axle brackets to adjust for the added length (or a spinde replacement kit on 2nd gen or later) with a shackle and add-a-leaf out back (good for 3-4"), then a spring over in the rear and some 6" brackets up front, with new springs, steering, and possibly radius arms (lots more work) (6" +), and finally totally replacing the front axle with a straight axle - adding coil overs, etc., plus whatever is needed out back (new spring packs, etc.) to get up to 8" + lift -- all of which can also be combined with an additional body lift for a total of around 12" lift.
Note well: After a couple inches lift of either sort, be prepared to spend some real money to do things right. There is NO SUCH THING as a cheesy lift - your safety and drivability depend on using well-engineered parts that work in concert with a well-designed and proven plan for lifting the truck. There will also be more drivability issues the higher you go - AND added expense for new gears, lockers, tires, etc., once you get your truck up in the air.
