From my experience, turbos and especially trochus are more apt to graze on the algae along the grass, but they still go along the rock as well. With a tank that size you can do quite a bit of snails (ideal amount would be around 20-30). Turbos get the biggest so I would suggest 4 or 5 of them, while trochus stay a bit smaller, so around 10 would probably do well.
Cerith and Nassarius (which i forgot to mention before) will stay more on the sand especially the nassarius which bury themselves into the sand, both are mostly nocturnal but are great for turning your sand. If you wanted to get them, perhaps around 10 of either of them, or a mixture of both would be fine too.
Besides snails you could get some crabs, like emerald crabs which do a wonderful job with bubble algae and hair algae. You also do hermits, but don't count on them for too much work with algae, they're more of a lazy scavenger.