For the best combination of sound, ease of use and value I recommend and endorse the Fishman range but if you have a particular requirement please contact me as I have fitted almost every generally available pickup.
I have recently been impressed by the MiSi pickup range.
The appeal of these is that they are active systems using the tried and tested LR Baggs Element transducer married to a preamp powered by a "super capacitor". Instead of constantly replacing batteries the MiSi user simply charges the capacitor for 60 seconds using the charger provided and this provides upwards of 8 hours playing time.