I'd vote for the grapple bucket to go with your LMB....
I have a grapple bucket, LMB and HD rock bucket. I do not have the utility grapple. IMO, the PowerTrac utility grapple is a VERY light-duty grapple, the way it is designed and reinforced.
Dedicated grapples, like the utility grapple, are great for handling brush or small logs -- but that is essentially ALL that they are good for. In comparison, the PT grapple bucket is VERY versatile. It is my single most used implement and stays on the tractor almost all the time.
Note that it has very agressive teeth, standard, and adding a toothbar isn't necessary. It digs and pulls roots out better than the HD rock bucket because it has much longer teeth (I sharpened the edges of the teeth on mine a little bit using a grinder), and it will still move a considerable amount of brush and grasp logs too big for the PT to carry...
Simple example of its versatility -- it is absolutely great for cleaning off the garden at the end of the season. Tilt the bucket, sinking the teeth a couple inches into the ground and backdrag across the garden until you've drug out a bucket load of debris (dead stems, and grass/weeds that've grown up, etc.). Then, stop back up a few feet and use the bucket to pick up that load and carry it to the "slow compost pile". Then repeat the process. The long, narrow teeth on the grapple bucket loosen enough topsoil doing this that you can then sow a cover crop if you'd like...
I also use the grapple bucket a lot to haul large objects in the bucket, using the grapple to hold the item in. It hauls a 55 gallon drum nicely, for example, without any need to strap or chain it in -- simply close the grapple on it gently. My friend uses it all the time to haul his little Troybilt tiller to the garden.
I use the LMB only for hauling stuff, mostly light materials -- topsoil or mulch (and I've spread literally tons of mulch). Since I got the grapple bucket, I don't use my HD rock bucket at all. I'm considering cutting it down someday and modifying it to work on my minihoe to clean out ditches, kinda ike a Gradeall.
Here's a video of my grapple bucket showing the amount of brush you can easily grab and move. IMO, it will "grapple" as much as most people will need, most of the time...
YouTube - Power Trac Grapple Bucket