Lol, asking a ball python community if you should buy a ball python or a sand boa?
I personally like some variety to my collection. I have more than just ball pythons. It is nice to keep different species! I think getting a young female to be the future mate to your male is a great idea. It's a few years down the road but its good to plan in advance! You can get a lot for under $300. Spider, Pin, Cinnamon, Mojave, Lesser....the list goes on.
It is ultimately up to you. Get the snake you like the most! It should be an easy decision when it really comes down to it.