1a, 1b, 2a, 2b are all correct and mean the same thing in the usual context. There is technically a very slight difference between 1 and 2, which is only relevant in very rare contexts - so rare it's barely worth mentioning. They practically always mean the same thing.
3 - they are all a bit different. 3a & 3b are technically valid. 3c wants a dash or semi-colon instead of a comma - it's currently sloppy grammar with that comma but not strictly wrong. 3d has multiple issues of unequivocally wrong grammar.