The difference is that one is elite in a couple of areas (Garland's shooting and ball handling) and the other isn't really more than just above average at anything (White). It takes some elite skills to be a great NBA player and as a prospect I would say Garland is very similar to Steph when he was coming out of college. Both great ballhandlers and shooters and similar in size and stature coming out of college. Both were considered score first guys that had shown some flashes of potential as a passer. Obviously Curry got better every year after enterring the league, but to me they are almost identical as prospects and have nearly identical perceived strengths and weaknesses.
I would guess that White might be a little safer as a pick, but I think Garland has a much higher ceiling if he comes along as a passer.