UGH THIS IS HARD
I think all of them would “get along” in the sense that I’m sure they could all work together to save the universe or whatever if the time called for it. Because they are adults and such. But in terms of who would exchange numbers and keep in touch later, hmmmm.
I think Martha Jones would get along with pretty much everyone always because she is Martha Jones and I think she’d be the best at letting things slide or holding her tongue if someone irritated her. (LOLOLOL I mean look at s3.) So I can see Martha being some level of friend with pretty much everyone. LOL, Martha’s probably the greatest friend too. Martha would totally remember your birthday even without Facebook reminders.
Rose, we saw Rose with Donna and Sarah Jane and she became friends with them, so… there’s that. Long-term, with Rose and Donna I find it hard to say because they’re never in a scenario where they’re in each other’s lives long-term and if you’re going AU about it there’s a lot of factors. If somehow JE had ended with Ten, Rose and Donna travelling together, for example, I think they’d be friends but I also think it’d get super awkward? The girlfriend and the BFF, there’d be a bit of jealousy on both sides I think. I think Rose and Martha could get along pretty well — they’re a bit closer in age, we see them appreciate each other in JE and I think once the residual weirdness was out of the way they’d have a lot of fun swapping stories about the Doctor and Mickey.
I could see Donna + Amy going either way. Donna has a really strong personality and I think she’d get along with lots of people but clash with some of them, and I’m not sure if Amy and Donna would get along really well or just clash really badly. They might also bring out each other’s insecurities, so idk. We saw Donna and River interact and they didn’t seem fond of each other, so. Donna + Martha, I think they have a lot of respect for each other and obviously they get along just fine as we saw, so I can see them being like casual text-message friends, but not super close.
I’m REALLY curious about the Ponds, because we have no real basis to draw from. TBH Rory seems barely interested in anyone whose name isn’t Amy Pond, so I think Rory would be unbothered but also unattached to any of the others. Amy knows she’s not the only person to have travelled with the Doctor, but I think she still thinks of herself as THE best friend, and even if that’s true with Eleven I think meeting someone like Donna or Sarah Jane would throw her for a loop. That said, I think she’d enjoy gossiping with Martha, Donna, Sarah Jane, etc. I think Amy and Rose would be a bit weird, though, because I think Amy would get a bit jealous on River’s behalf.
River… I see people say that River isn’t the jealous type, but she gets jealous of herself in those s6 boxset specials, so idk. I think she and Rose would be especially strained because they both represent something very sad for each other — the Doctor ~*moving on*~ in Rose’s case, and the Doctor not knowing her/the Doctor “before” her for River. I mean I don’t think they’d hate each other, I think they’d respect each other and I think they’d both accept the reality of stuff, and Rose has Cloen so I don’t think she’d be THAT crushed, but it would still be a harsh reality to face that I think would make them uncomfortable around each other. And the same kind of goes for all of Ten’s companions with River, I think — they all represent this period of time that terrifies her because she’s not in the Doctor’s life anymore, so I think that would unsettle her even if on a personal level y’know she thinks Martha Jones is a cool lady or whatever.
Jack loves everyone. Jack and River would probably get on like gangbusters which would horrify the Doctor forever and always.
I may have missed some combinations in here LOLOL. I talked a lot about how their relationship with the Doctor would factor into their relationship with each other, but I think that’s a pretty significant point because he’s the common link that would bring them together and in a lot of cases he’d be the main thing they’d have in common. I don’t think for instance if most of these people met on the street they’d be fast friends just because they all come from such different backgrounds and stuff.