Dthrow is easier to DI out of so it's only really usable at low percentages OR if you notice your opponent always DIs in front of you at mid percents. It's also an okay DI mixup if you get a grab facing away from the ledge, but it doesn't really lead into anything (maybe uair?) at percentages where bthrow will actually kill.
Uthrow combos at lowish percentages are usually slightly suboptimal (eg. uthrow bair bair is slightly worse than dthrow bair bair BUT it seemingly works up to a slightly higher percentage, uthrow dair isn't guaranteed while dthrow dair is, etc.) but at higher percentages they're basically unavoidable when dthrow combos become quite difficult to connect.
Uthrow is Diddy's least damaging throw and uair is Diddy's least damaging aerial so avoid uthrow uair outside of kill percents (~130%, try to stale uthrow but not uair). Uthrow bair (9%) or fair (10/8%) are your most valuable options aside from reading an airdodge. Also remember that stage positioning is important too, bthrow alone does more % than uthrow uair so it's worth using particularly if it puts your opponent offstage.
tl;dr downthrow until it stops working or you can only get an uair, then uthrow fair/bair