Such an underrated pairing yet this is my favorite Spike x Mane 6 shipping.
Let me explain why: When Spike and Twilight first arrive to Ponyville, Spike likes Pinkie right away and even joins the party in the library.
In "Feeling Pinkie Keen" Spike believes Pinkie Pie about her pinkie sense right away. In "Over A Barrel" Spike plays the piano for Pinkie Pie during the whole "Gotta share and gotta care" song, and he is the only one who claps for her at the end. In "It's About Time" Spike recommends Twilight to see "Madame Pinkie Pie" to see the future. All together though, they always seem to have fun together. I think it's cute