1) Donna Noble
It’s incredibly tough to chose the finest companion to grace the modern series of Doctor Who, but one candidate has to be Catherine Tate’s big-mouthed, big-hearted Donna Noble.
Going by her initial appearance as a comic relief bride who accidentally gets transported to the TARDIS, we would never have thought that Donna would make a great companion. However, when brought back for season 4, Donna’s character grew, organically yet exponentially, into someone with a lot more depth. It became clear that Donna’s sharp tongue was just a symptom of her own insecurity. Yet over her travels she became, as the Doctor put it, “the most important woman in the whole wide universe.”
Perhaps the best thing about Donna, though, is her brilliantly unfussy relationship with the Doctor. Unlike a lot of modern Doctor-companion dynamics, theirs was purely that of two best friends without any complicated romantic feelings cluttering up the TARDIS. Donna also acted as the Doctor’s conscience on many an occasion: most notably, when she convinced him to save a family from the destruction of Pompeii.
That’s Donna for you – the noblest Doctor Who companion of them all.