If you use the 14 or 12/4 cables you will have two 2 wire circuits.

That is 4 current carrying conductors.

The neutral of a two wire circuit is always considered by the NEC to be a current carrying conductor.

If you ran these two circuits using a multiwire branch circuit in 12 or 14/3 from a 240/120 service you would only have two current carrying conductors as the neutral will only carry the imbalance of current between the two circuits.

Bob Badger
Construction & Maintenance Electrician