As CourageHound said, I see if it is cool or not.
I remember that when I played the third Generation, I was so excited to catch a Bagon! Even if I didn't know its evolutions, I was so glad to catch that Bagon, because it is simply cute and a baby Dragon. When I saw its first Evolution, I was like, ow...Not pretty as I thought. When I saw Salamence, I was so happy to see it, even when I saw the Pokédex entry of Bagon, that it dreamt one day to fly across the sky...And when I saw that Salamence have its own wings I was so happy for my Bagon :3
Due to its dream and its good looking I took Bagon!
I remember about Trapinch, it was the same thing...Exactly the same thing!
I was happy to get two useful Pokémon and in the same time, that they're well designed :3