Unflavored waxy maize or karbolyn. Both work the same but I like the thicker texture of karbolyn better when mixed with whey. Tastes better mixed with fruity flavored protein vs chocolate based flavors.
If you want something faster then HBCD's. If you want to reduce the cost you could add it in a mix with either dextrose, maltodextrin, coconut sugar, honey etc. Although for me if it's a meal replacement shake through the day I prefer using activated barley or oats (or a mix of both). They will take longer to digest but that to me is a good thing.