Ron has neuroses based on how he sees himself compared to his siblings…

Bill? 

He’s the oldest. The coolest. The one who set the standard; prefect, head-boy, later went on to a well-paying job and married Fleur Delacour. Bill is the sibling Ron probably aspires to be the most; cool, handsome, intelligent, wealthy and attractive to women. 

This is possibly brought to it’s prominence during the Christmas break in Ron’s sixth year. Bill is Fleur’s fiance by this point, and Ron is desperately trying to seem accommodating to Fleur (whether this is because of Fleur’s Veela ancestry having an unintentional effect on Ron or just Ron trying to be friendly is never explicitly confirmed). On each occasion, Ron is seen as ‘less impressive’ than his brother, and (in case) he is left sprawling in the dirt after Ginny trips him up (which we’ll come back to later). 

Percy? 

The Weasley brother that Ron is possibly the least like. Where Percy is rule-following, Ron is a rule-breaker. Where Percy is studious, Ron is lazy. Ron started at Hogwarts with a second-hand wand and robes; whilst Percy was given brand-new robes and a new pet because he’d been made a prefect. 

During the whole of OOTP, Ron unconsciously compares himself to Percy; as he is the first Weasley sibling to become a prefect after him. Ron is terrified that people (especially Fred and George) will see him in the same way Ron saw Percy; as a stuck-in-the-mud, pretentious busybody. 

Fred and George?

Out of all of his siblings, Ron probably has the least consistently-stable relationship with the twins. They were his original bullies; the siblings who burned a hole through his tongue, used his childhood pet for bludger practice, and gave him his arachnophobia (something that is often used to mock him throughout the series). It’s noticeable that Ron spends most of fifth year avoiding using his prefect abilities in front of them, because he knew that they would make his life h*ll if he so much as acted a little like Percy did. He doesn’t worry about this in front of everyone-else; Fred and George clearly inspire so much dread in him. It’s also noticeable that his self-confidence improves significantly after the twins leave Hogwarts.  

Ginny? 

Probably the most complicated. Growing up, Ron was closest with Ginny. They were the babies of the family, and had a much smaller age gap between them than Ron had to Fred and George. They clearly had a close relationship; given that (throughout the whole of Ginny’s first year) Ron is the sibling that gives her the most attention and support (Percy tends to be a little more parental in his approach, and the twins tend to make rude jokes a lot). 

However, it becomes obvious that Ginny is clearly favoured more by Mrs Weasley. As the first girl in the Weasley family for generations, she has a novelty than Ron simply doesn’t have. It’s never stated, but it cannot be a coincidence that Arthur and Molly stopped having children after Ginny. They (although I think Molly more than Arthur) were aiming for a girl for years, possibly since Percy was born. There’s a reason the Horcrux brought up the fact that Ron suspected that his mother craved a daughter; he always half-suspected that he was less loved than his sister was. 

There is also the noticeable fact that everyone (aside from Harry and Hermione) seem to prefer Ginny over Ron.  She’s considered a beauty and is incredibly popular; a far cry from Ron’s utter lack of romantic attention (aside from Hermione, and-to a lesser extent- Luna) prior to sixth year, as well as Ron constantly being (unintentionally) overshadowed by his two best friends. 

Heck, even the Hogwarts teachers seem to prefer Ginny to Ron. Slughorn invites Ginny to become a member of ‘the slug club’ largely because she jinxed Zacharias Smith, whilst Ron was entirely ignored by Slughorn throughout the entirety of sixth year (even after Ron is poisoned in Slughorn’s presence, the professor still can’t remember his name).  

Part of this I can chalk down to JK Rowling’s sudden change of characterisation for Ron and Ginny’s relationship. Whereas previously they had a close-but-banterish relationship, in HBP they are suddenly at each-other’s throats a lot of the time. Most of this tends to be from Ginny outright insulting, belittling or humiliating Ron (often in the presence of women Ron is attracted to). It’s never stated why their relationship suddenly went sour, but (within the larger narrative) it’s possible that Ginny was going through a rebellious phrase, and Ron happened to be the most obvious target for that (being the sole older brother left at Hogwarts by HBP). I personally find it uncomfortable to read about, as it often goes beyond usual-sibling teasing and into borderline-bullying (since it often relates to Ron’s insecurities). 

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(You’ll notice that I left Charlie out. Maybe it’s just my own personal readings speaking, but I always felt that Charlie was possibly Ron’s favourite brother. Unlike their other siblings, Charlie is very relaxed and mild-mannered. He’s also a massive fan of Quidditch just like Ron. Charlie might have the coolest job on the planet, but he’s also a really down-to-earth person, even by Weasley standards. I think Ron really liked him for that reason. I actually have a fic in the works about Charlie noticing Ron’s insecurities about how he saw himself compared to their other siblings, so watch this space…)