Simon - I've been using La Bella 2001 Extra Hards for over 10 years now. I've tried other strings, but I've found La Bellas to have the sweetest trebles of everything I've tried on my guitar. I like Extra Hards because of the clarity of the basses as well. D'Addario are great strings, but a bit "average" in terms of the tone of the string. However, if I were to get a new guitar, I'd spend a great deal of time trying to find the tension/brand of string that works best for that guitar.
If you an afford it, get a bunch of different strings to try out and A/B the sound of them. See what you like!
Nick Cutroneo - Classical Guitarist, performer/teacher/suzuki instructor