Obviously we will have to agree to disagree, I spent quite some time examining the question and was able to come to an answer, for me the experience was that the more I looked into the matter the clearer the picture became until I reached a point that I felt the answer to who was correct was obvious.
I am hoping that if I continue looking, real truth might be under all the convolution.
My current line of thinking is this. One must be in error. IF one is in error, I feel based on study that it is more likely RCC that has it wrong, as compared to EO. (cue the RC protest here, but plain view of it is that RCC is further in left field as compared to EO.)
now, Looking at Orthodox, I still cannot fathom a church that "has it all right." I do not believe the promise of Christ states anything about error being kept from any one organization.
these points are what stick in my head.
1) the promise about the gates of hell do not state perfection. This is a claim of interpretation, the text does not state as such.
2) being able to trace "apostolic succession" back to the first century imparts nothing towards the assertion that there is no error. Any single one of the fallible men over the years could insert error. Having a long line of succession does nothing to preserve truth.
3) many teachings of the EO are extra biblical, and I have no assurance that they are not false, given the above 2 points. They all hinge on a promise that I do not believe was ever given.
4) I have seen God work very powerfully in the lives of people who have nothing to do with EO or RCC. If either were the "only" church, I would think I would see much less of this outside of the "one true church." I would also think that if so many people were seeking God earnestly, and depending on the Holy Spirit, and there WAS a "one true church" that they would be drawn to it indelibly. I believe God would be monsterous if he had those calling on his name earnestly, and not guiding them to his "one true church" if it existed.
5) The main thrust of the bible is salvation by grace, and that what God considers pure and perfect have nothing to do with ritual and liturgy. (personal observation, subjective.)
there are more, but these are some of the main points of my reasoning.