This months Beer52 box contained a rather exciting experiment which highlights the difference that a single ingredient can make.
Exactly the same reason for building Brewnode.
Malt
Ruby Rising v 11th Hour
Both beers have Caramalt, Amber Malt, and Pilsner Malt. 11th hour has the addition of rye malt. The differences were surprising. The rye dramatically increased the head foam and its retention. It also caused a slight haze. Overall it seemed more rounded and suited the style. 
Yeast
California Dreaming v Dreaming of Frites.
No surprises here. The Abbey yeast gave a saison nose and correspondingly typical flavour. It also made the beer a bit darker and slightly better head retention.
Zig v Zag
Zig used a Belgian abbey yeast and Zag was T-58 (whatever that means). In my mind, Zig was the clearly the better beer. It had a sweet, fruity aroma and a more rounded mouth feel than Zag. Most significantly, Zag retained no head foam and was clearly less effervescent.
Hops
Mosaic v Ekuanot
Well this one is all about the nose. I preferred the Mosaic because it was more floral and slightly sweet smelling.The Ekuanot was not as powerful and had a medicinal edge to it. Mosaic has a stronger aftertaste but was less bitter than Ekuanot. 
One thing that came as a surprise was that the Ekuanot had better head retention. I don’t understand how hops can have this effect. I definitely need to do some more research on this.
Conclusions
- Amber malt increased the head retention but introduced a slight haze.
- Hops can effect head foam. How?
- Avoid the Belgian blonde yeast, T-58.