Blacks can be slightly more bitey than silents, however there is now a species of brown cricket being used (the Jamaican field's) that are much more aggressive. There is also a slight difference in nutrition between the 2, although not that substantial.
The best thing you can do is to provide a bit of everything to your dragon. Crickets (black and brown), locusts, mealworms/morios, calciworms, silk worms, butter worms, cockroach species etc. The more variety you provide, the less likely you will have any nutrition-related problems (which are very common!)
Locusts will have a problem getting up the tubes depending on their size. I just keep them in the tubs they come in. Also I've heard that crickets can escape from cricket keepers; have a search on here, there have definitely been threads about it.