i firmly believe God is working in all the churches.
that is very different to the 'branch theory' or 'unity of heart' theory which says that all (protestant, catholic and orthodox) churches are simply different and equally valid ways of worshipping the same God.
the orthodox church (and here i include eastern and oriental orthodox churches, as we have agreed on the same doctrine) is the place where the theology makes sense, the sacraments are correct and the clergy (generally speaking) will help you to have a closer relationship with God.
in other churches you can relate to God, but this is usually despite, not because of, the theology and practices of the church.
in churches which are not orthodox, you can learn a lot about God, but also be confused by wrong theology.
i believe you won't find a really deep relationship with God outside of orthodox baptism, chrismation and Holy Communion.
when i was protestant, i was a sincere Christian believer, but i lacked a deep and sure faith and a deep peace.
now, as an orthodox Christian, all that i hear in church makes sense (i don't understand everything yet!) and i don't have to 'screen out' annoying doctrines or practices and close my eyes and just pray in the services. (i used to think it was 'normal' to have to do that in all churches!)
i am free to look and explore, because i have the writings of the early church fathers, the sacraments of the church and the lessons learnt from the life of the saints to guide me.
(see hebrews 13:7-8).
i found a community whose living faith guided all their decision making and taught them how to stay strong and forgiving despite all the troubles they went through.
so, dear friend, these are some principles to help you find your way.
i didn't join the catholic church because i could not find enough evidence in the life of the early church fathers or in the Bible to support purgatory or the immaculate conception of saint mary (without the inherited sin that they and the protestants think we all get). i also found, in my personal experience, that many of the people in the church i attended for a while did not have a deep personal experience of God. they saw church as a 'sunday' thing, and, although they were sad that they didn't have the desire to learn more about God, they didn't see how to resolve that problem. i had some interesting discussions with some of them, as i joined the orthodox church (meeting on saturdays in a rented building) during that period of several months that i attended the catholic church most sundays (and often the anglican church, but that's another story!)
i even asked the catholic priest at one stage why i couldn't be catholic, as i believed more of the shorter catechism than most of his parishioners did! (i was wondering at the time if the branch theory could be true, and the priest's wise refusal was one of the markers that i was on the wrong path!)
i slowly realised that the catholic and orthodox theology was not the same, and that i believed orthodox theology, so i joined the orthodox church (with the help of a very wise orthodox priest, who patiently waited for me to get my head sorted).
i believe God was leading me before i was orthodox.
God wants everyone to be closer to Him, and if there is not a strong and loving orthodox church that a person can get to, i think God leads people through other churches as part of their spiritual journey.
it was much better for me being protestant for most of my childhood, than being an atheist in a stressful personal situation with plenty of immoral and illegal distractions available for me. i think without my early non orthodox experiences of God, i could have easily been a prostitute or on drugs, and that would have given me much pain and heart ache.
i believe that many of the catholic and protestant 'saints' were close to God in their lives, using the resources they had available to them (sometimes they were not able to access the orthodox church). God rewards them based on their motives (only He knows) and what they did with what they had available.
i believe some of them are there in heaven with the orthodox saints, praying that people make wiser choices and asking God to guide us.
even john calvin repented on his death bed, so perhaps he is there too, praying for those who have made an even worse mess of his doctrines than he did, and asking God to guide people into the orthodox church.
on the other hand, some orthodox churches (eg the official churches in communist times in russia) drifted so far from orthodox beliefs as to not be useful to the people who went there.
so it is not a simple answer, nor a short answer!
it is also only my experience, and not a postgraduate view from a brilliant scholar.
but i pray God will guide you, and please take time to make your decision.
you can get closer to God every day, not matter which church you are in currently, and as you do this, He will guide you to the right place. (obviously i think this is the orthodox church, but i think the advice holds true, even ignoring my bias).
during this time, study the Bible, read the lives of the pre schism church fathers and saints and pray.
and don't rush!