Minor spoilers for episode 205 "Victory of the Daleks"
For someone with access to all Time and Space the Doctor seems remarkably taken with the little backwater called Earth. He visits here repeatedly and usually chooses companions from here to join him. The cynical could say that that is simply due to the television budget and the need for human actors but the show itself suggests there may be other deeper reasons.
One thing we know is that despite his mixed feelings for his own species he does miss them and has mentioned a few times that humans look like them. This has yet to be explained beyond it being a glib response, but there may well be distant history. In Doctor Who, more than life, almost nothing is a coincidence.
The Doctor (and seemingly all Time Lords we have met) have a flaw when it comes to emotional response. They tend to understand the extremes but totally fail at the subleties. Most of the incarnations of The Doctor have "quirky" personalities, most of which are due to inappropriate emotional responses, the type of emotion varying with the incarnation.
In "Victory of the Daleks" The Doctor attempts to convince a robot that it is human, but he can't. He lists things which should invite an emotional response and do to a small extent, but as Amy takes over it's clear that he simply doesn't get it. He understands Hate towards the Daleks fairly well but fails at anything gentler.
I believe that rather than simply travelling with humans because they remind him of Time Lords, The Doctor travels with humans because they _don't_, because they show something more that he cannot quite grasp, something he is searching for to complete himself with.