Should I get 1.0 or 1.2 Open Beta? I've had problems with Open Beta but I don't rmember about 1.0...which one is the most stable one with almost not bugs that will screw your game up?

IMO, neither. Use FWE instead. Just a word of advice, there is a reason they are in Beta. This is so there are a lot of people testing it and reporting bugs. If that is what you wish, by all means use 1.2 and report problems you will have to the report forum at Fallout3 nexus.