A thumb/bucket, I have found, are easier to replace and service than grapples. They're cheaper to replace. Hendricks has a tremendously strong bucket. If you have new teeth and cutting edges they'll last a long time. Not recommend for steel though!
Call an equipment dealer and see the difference. Most likely they will have buckets in stock but not grapples.

I believe the fixed grapple in the proper hands is the most versatile tool. I have seen too many slewing rings break on anything that rotates for demolition. DH Blattner in Minnesota has the first rotating shear from Labounty. The cutting edgea are great but the slewing ring always puked!
A bucket and thumb are another more economical tool. I demo'd an 8 story building with one and was very impressed because you can sneak between the rebar with the bucket and grab concrete with the thumb.