We have sheep and goats (along with horses and llamas) running in the same pasture, and sharing the same area of the barn. They all get along perfectly. WHEN I do need to grain I put the goats feed in an area the sheep can not get---(don't want the sheep to get the copper)...They all eat outta the same hay feeders though and get along great...When on pasture they get along great as well.. I have yet to have any problems with the goat/sheep being together...Actually our pygmy buck Houdini and our shetland/black welsh ram Shake-N-Bake are the best of friends. They are always together and seem to talk back and forth. They from day one have been like this and never fought with each other...
We at times will take a few sheep or goats (which ever seems to want to be out) and put them along the ditch lines to eat up the tall grasses and weeds. Then bring them back in at nigt. I don't leave the tied out at night for their own safety. Our horse does a wonderful job of eatting the grasses down along the ditch as well. I haven't tried the llama yet, as sometimes she doesn't like to be haltered....
I personally think either would be good weed/grass controllers for you. Do you plan on breeding--what about the babies, or milking any does??? I guess I would look at questions like those first before making the final choice....But if you ask me....I would say get both...lol