They are so different and fulfill two very different needs. Are you asking, "Which should I buy first?"
Then the answer would always be shotgun. At least in my world, with my 2 cents.
.45acp, .40 S&W, 9mm, .38 Spl, .380 acp, 22lr
12 gauge, .223/5.56x45mm, 30-30 Winchester
2 Chron. 7:14 Christians must seek His face