The 11th Doctor spent his first day with a child... with the fitting-situation-regeneration in mind, that explains allot... for example why he is so protective, but still so playful, that's how a good caregiver acts. also this explains some of the littler things, like why bunk-beds were chosen for Amy and Rory over a double bed. Now personally the 11th Doctor is my favorite, and I respect if you disagree with me, but this explains allot about his character.
Now, the 10th doctor is kind of interesting... his regeneration was "special"... his regeneration was caused by taking the power of the tardis 4th dimensional access core (yes, that's how it works... it access the 4th dimension (time) and then moves the tardis through the 4th) through Rose while she was a 4th dimensional being (yes, that is what she was)... so while he was regenerating he was literally split between dimensions moving slowly into the 3rd dimension completely... this kind of explains his character, the 10th doctor was the more knowledgeable, strategic, logical one of the 3... and this is because while he was regenerating he literally had knowledge of all of time, he could more then think ahead... he could see forward in time, and this explains him allot.
Now we never got to see how the 8th Doctor died and how John Hurt Doctor died (well, at least we haven't seen it yet) and how it eventually led to this Doctor, the 9th... however we do know that this doctor was born around the end of the Time War. so he was born in War... a big war for that matter... at that kind of explains his militaristic attitude... and his stern-ness... it also explains his "EVERYBODY LIVES" attitude... it seems as if the war kind of scared him, if you will...
this is kind of awesome... I absolutely love how the continued to make sure that 1st day influenced there entire personality... things like this is one of the many reasons why I love Doctor Who...