Buy from a reputable dealer. If you buy from a show or store make sure you know how to look a snake over and visually check his health. Make sure you know where a herp vet is in your area so you can get a fecal exam done on your new snake. Read up on husbandry for BP and make sure you have the snakes environment set up prior to getting the snake. Proper size home, heat supply, thermometer, and thermostat et... Get the temps and humidity regulated and you are ready to go shopping.

Read all the care sheets here, then search google for more information. If possible get the Ball Python Manual (a book) and read it first.

I would get whatever snake you like the best that is in your price range. Look for a snake that is healthy and has a good temperment. This will vary from snake to snake, not morph to morph IMO, though someone may insight on this I am unaware of. Make sure you are prepared to care for the snake for the next 30 years. Ask questions, check out the different morphs online and see what you like. Educate yourself and enjoy!

Congradulations on making good grades. I like the different variations of Pastels myself and a Mojave would be my second choice. If you are not breeding, just get the Morph you like the best.