Science says that the differences are,

1. Bisexual colors match my eyes better
2. Pansexual is better for hooking up with nonbinary, trans and polyamorous people
3. Bisexual is better for hooking up with binary and monosexual people
4. Pansexual colors look better when painting walls

Similarities,

1. Both describe sluts and whores
2. Both describe me depending on who I’m trying to sex