Who do you think it's closer to Rukia, Renji or Ichigo??

I'm going to write this without speculating on romantic relationships, regardless of who I personally want to end up with who. For me, this will be more on terms of friendship than anything else. (This is also off the top of my head, so forgive me if its confusing. >.< )

So, removing that sticky matter out of the way, as it can be argued over until the cows come home, my answer is quite simple.

Both.

For Renji:

Its true that Renji has known Rukia the longest. I believe that the time they spent together helped to shape them into who they are now. Yes, I get that Renji all but ignored her for many years, but I also feel that he was doing what he felt was best for her. They both grew up without families, and I believe in his mind, if he were to try to come between her and her new family, it would take away something that he felt she needed. He wanted her to be happy with a family that neither one of them had growing up.

I also feel that he had no qualms in going to Earth to bring her back because he honestly believed that at the most she would face some jail time. He even asked her if she wanted to add time to her sentence for just touching Ichigo, and was very adamant in keeping her from doing so. So I believe he went to get her, not to get her into trouble, but to minimize the amount of trouble she would be in had she stayed longer. Even if he had been sent after being told that she would be executed, he had been absolutely convinced that Byakuya wouldn't allow his sister to be executed, and seemed truly shocked when he found out otherwise.

And then he was able to swallow his pride and beg his enemy to save his best friend. The same enemy, I might add, who had just recently defeated him in a battle of ponytail-holder-losing epic proportions. That takes both courage and guts, imo.

And then he turned on not only his Captain, but practically every one else around him to help rescue and keep Rukia safe.

So my take on Renji's relationship toward Rukia: He loves her (whether or not romantically is up to someone else to decide :P)

For Ichigo:

Rukia is the embodiment for the second largest change in Ichigo's life. (The first being his mommy ;_; ) She gave him the means to save his family, tore his life upside down, and opened the doorway to help him achieve the ability to protect... everyone if he wanted to.

Yes, they annoyed the living snot out of each other at first (and still do, to an extent) but to be honest, I have wanted to strangle each and every one of my best friends and loved ones at times and I would still do anything for them.

She was the first to teach him the ways of being a shinigami (...with leaving a lot of it out) and he was the first to teach her how to do small stuff like putting the straw in her juice. (Grah, those things still give me problems...)

Ichigo spent the majority of his later life (every since his mother, again) protecting everyone else. I think that when she ran off to keep him safe, it was the first time that someone else openly protected him. (To avoid dispute, I saw his and Chad's relationship in terms of fighting as a sort of symbiotic protection plan.) The last person who seemingly put no thought in their safetly in exchange for his was his mother. To be clear, though, I'm not saying he has an Oedipus complex. This is why, I believe, was one of the main factors as to why he went to Soul Society to save her. This time, he had the power to possibly save the person who had protected him. I believe he would have gone anyway, because she was a friend, they did have a bond, even if they hadn't known each other for very long.

Then, at the end of the Rescue arc, when all was said and done, you could see he was trying his best not to interfere with her decision on staying behind. (This is taken from the anime. At the end of the episode, when she announces her decision, there is a close up shop of his hand. You can see he barely refrains from making a fist or some other gesture to try to convince her to leave.)

I know that I only really covered the Soul Society arc here. I'd try to write more, but right now my brain's going '...Seriously? And this isn't even a paper for school? If you'd put half as much thought into those things, we'd be on the Dean's List, you dweeb.'

I'll just leave off for now with a theory that if none of them got together in a romantic sense, I can easily picture the three of them sharing a three bedroom apartment, living in discordant harmony, and arguing over whose turn it was to burn dinner that night.