I would guess that NAND and NOR might better lend themselves to practical physical implementation.
Also: If you don't limit yourself to 2-input/1-output gates, there's loads more universal gates. Many 3-in/3-out reversible gates are universal [1]. I really have a soft spot for the Fredkin, it just seems so elegant.
Also: If you don't limit yourself to 2-input/1-output gates, there's loads more universal gates. Many 3-in/3-out reversible gates are universal [1]. I really have a soft spot for the Fredkin, it just seems so elegant.
[1] http://www.thefullwiki.org/Three-input_universal_logic_gate