"I'm going to order from The Attitude, are they safe? "

As safe as any, not one complaint on this board.

"Discreet? Also, how long does shipping usually take to the US?"

Yes. A couple of weeks.

From the US use a false name and a drop mail box.

"Do you think I should grow this Hindu Kush versus growing Lowryder? "

Only you know the high/stone that you want. If the plant will fit within your growing constraints and give you the effects you want give it a try, it won't be the last time you order seeds.