Well, you're on the right track by first defining your need; that is, how you intend to use the tool.
In fairness, you will probably end up getting two, or even three, of these tools, for different size jobs.
For most of your needs, including core drilling up to 2 1/2", an "SDS" drive tool - the smallest of the batch- is fine. The tool is reasonably lightweight and handles well on a ladder.
The next step up is the "SDS Max" and "Spline" drives. These have a larger diameter drive shaft, and are used for more demanding jobs. They are the smallest tools to be of any help in driving ground rods, and a driving attachment is available (Use it!).
It seems that there is more available in "SDS Max" than "spline."
The final category are "demolition hammers." These tools hammer only, they do not drill. They are very effective in breaking concrete and driving ground rods- though hauling even the smallest (35 lb.) up a ladder is no fun. Typically, they use 1 1/8" hex shank tools.
All of these tols are pricey. While this forum has had many opinions expressed as to brands, I suggest that you rent various models, and find your own preferences before you part with the cash.
