Please no biased answers (unless you state it is your opinion :p).
I don't understand how are you not going to get biased answers in this matter.
Everyone loves to call he is just Muslim, and if you ask him how is that, he says, it is possible by being a Sunni Muslim. If you ask the same question to someone else, he would say, Shias are the only true Muslims out there. Suffis consider all others don't know anything about Islam except them.
This thing is solely opinion based.
As for this...
What are the principle/fundamental differences between Sunni and Shia?
That's a way too broad question. But as far as I've seen...
In the Sunni branch of Islam, the canonical hadith collections are the six books, of which Sahih al-Bukhari and Sahih Muslim generally have the highest status. The other books are Sunan Abu Dawood, Jami` at-Tirmidhi, Al-Sunan al-Sughra and Sunan ibn Majah. However the Malikis, one of the five Sunni "schools of thought" (madhhabs), traditionally reject Sunan ibn Majah and assert the canonical status of Muwatta Imam Malik.
In the Shi'a branch of Islam, the canonical hadith collections are the Four Books: Kitab al-Kafi, Man la yahduruhu al-Faqih, Tahdhib al-Ahkam, and Al-Istibsar. (Hadith)
There lies the main difference I can say. The Hadith which Sunnis consider to be authentic (directly from the mouth of Prophet Muhammad(pbuh)) are not considered to be authentic by Shias and vice versa. This can be the main root to today's disparities between Shia and Sunni beliefs. But back then, you know, it is politics.
why there is so much conflict between both sects and the major religious difference?
Ego and Shaitan
I would personally call myself a Muslim rather than label myself as Sunni/Shia/Suffi etc...
Yeah even me too.
May the creator guide us all.
Note: This answer is not to hurt any sect/madhab, and opinions stated above are just randomly formulated.