I love the penhaligons stuff and my personal favourites are:
Opus : full of complex layers, almost has a kind of black pepper backing to it, very classy and my girlfriend absolutely loves it.
Endymion : Rich, sweet and spicy. Good lasting power. Kind of like Givenchy's Xeryus Rouge but more classy
Castille : Aqua Di Parma basically. Good long lasting and clean smell. Another hit with the girlfriend.
Quercus : CKone with a bit more complexity. Doesnt last long on me though, as its only a cologne.
if i could only ever have two, it'd be opus and endymion all day long. if i could have 3, i'd add castille into the mix.
English Fern : I like this one, but don't have huge amounts of experience with it, as I only had a sample size. But its certainly a good clean, fresh smell with lots of green notes.
Blenheim : not one i'm a huge fan of, in spite of its heritage.