If your intention was to give Sadaqa for the poor and needy, then you have to give it to a poor or needy after being sure that they are poor and needy. Many of those who beg on the streets are not needy, so giving hem will not fulfill your responsibility to give to the poor.
If your intention was to give Sadaqa for any good cause, then you can give it to orphanage, Masjid, Imambargah or any good cause including poor and needy.
Wassalam.