Needle first. She isn't just a basic plain jane, she's a person with a genuine drive for helping people, that however noticed herself getting sidelined more and more as the episodes went on, with her closest thing she had for friends either getting eliminated early (TD) or hitting it off with someone else more than her(Coiny).

After bouncing from team to team in an effort to not disappoint anyone (and therefore not ruin any of her newfound, or newly mended relationships), Needle became more jaded, feeling like everyone saw her more as a tool than a genuine friend or ally. They didn't really want her as her... they just wanted her strengths. And she decided that enough was enough.

In BFDIA23, she was a lone wolf for the most part, only relying on herself because she didn't want to open herself up to someone only to get used yet again. Pencil gets through to her a little... but really, it's more because of Freesmart generally being the least worst thing Needle currently has.

Now let's tackle Tennis Ball. I fear he is one of the most misunderstood characters in the show. Possibly more than Pin was, as her suffering being so plain to see at least got her some degree of empathy from the audience, while Tennis Ball is watered down in the fandom as a mean manchild who simps for GB and hurts Book and Needle.

Tennis Ball's story is an arc. A corruption arc. He is, indeed, not morally good. However, he didn't "suddenly turn evil" like some people in the fandom say! In fact this arc has been building up ever since BFDIA8. You can check out this analysis I already wrote on him on Reddit if you want more information, but I'll briefly summarise it here.

Tennis Ball has long suffered with an inferiority complex regarding his inventive skills compared to Golf Ball, which hasn't exactly been helped by her uncompromising and even bossy demeanour in regards to him as well. However, even if their friendship isn't perfect, each of them work as a balancing force for the other: as an example, TB has always been very receptive to praise and has the ability to become a bit too full of himself if he doesn't have Golf Ball to keem him humble, even if she does so by overly strict means sometimes He still admires her a lot and feels indebted towards her, and wants to make her proud.

When BFDIA14 hits and she gets eliminated, Nickel comes in, and in a way briefly acts as a substitute for Golf Ball, even if he does it through sillyness instead of strictness. However, when Nickel gets eliminated too and Tennis Ball is left to his own devices, he realises how heavily the deck is stacked against him and how most of the remaining participants get through by sabotaging each other.

While Golf Ball might disapprove of his methods, TB has been cheered on by a lot of his now eliminated former teammates, which further proves him that his dubiously moral methods are accepted and should be used to their fullest. Although in BFDIA23 he only mentions GB, since she is his closest connection, you better believe all the support and validation from everyone else has also played a part.

TB doesn't want to be mean to hurt people, he doesn't enjoy tormenting Book or Needle because he hates them; remember he actually wanted to work with Needle but kept being rejected by her over and over, until he realised that if he didn't strike back she would walk all over him. He is indeed not a villain, even if he does villainous actions!

In fact, I think Tennis Ball and Needle have a similar theme of starting off as someone else's sidekick and trying to become their own person by acting in ways they wouldn't previously have considered.

I think a finale between the two of them would have been great, with the way they contrast each other and their relationship going from friend-ish to outright rivalry. However, that obviously can't be done, and I know one of them will be chosen and the other will be eliminated.

And yet, I still believe you can root for a character without bringing the other down. I understand voting propaganda is a unremovable part of the BFDI fandom, and it's great to see people talk about their favourite characters' upsides and why they deserve to stay. However, you can do that without watering the other character down or misconstruing them into a flat cardboard cutout with no nuance.

I'm not sure if this post will reach the people I want it to reach... but I hope it does. Please be kind to each other. They are all winners in our hearts, anyways.