I mostly see Twilight Sparkle as a mother to Spike, but I sometimes see the rest of the Mane Six acting as mother figures to Spike sometimes. If you had to rank the other ponies on how motherly they act to Spike, most motherly to least motherly, how would you rank them and why? :-)

Fluttershy
Applejack
Rarity
Rainbow Dash
Pinkie Pie

2404108 None, 'cause they don't act motherly to him at all, in fact: they barely talk to him, or, they make fun of him. Do watch the show?

: really cares about him in manly episodes
: love interest who's very possessif towards him
: great loyalty and very protective (Dragon Quest)
: they're like thief in fair when they teamed up together
: acting like a awkwardly obsessed friend

2404144 Pinkie Pie also taught Spike how to break the fourth wall. To make up for unintentionally harassing him since the "Party of One" ficaso.

2404108 Because Twilight had so much free time to raise him while studying under Celestia. Because you would give a twelve year old girl a new born dragon to raise by herself. Because Twilight and Spike never pick on each other like a brother and sister do. Because L. Faust never said that Celestia raised Spike. So of course Twilight is Spike's mother.