6.1 is going to be the better core since it has been released and used on many phones. 6.5 still has bugs that need to be fixed and will be once official 6.5 roms start to come out. I like the functionality of titanium better than TF3D and the new start menu design being finger friendly doesn't require use of the stylus for those with big fingers. The best thing you can do to get your questions answered completely though is flash a 6.5 rom and try it out. We can tell you everything about it but you need to actual experience to make the decision of what system to run.