I use Baggs LB6 bridge with internal preamp on my Buscarino Starlight nylon (my most played guitar at the mo’). It is astonishingly easy to get a good sound in a variety of spaces, from teaching studio to noisy exhibition hall. It’s has an active preamp on the end pin jack, so battery needed. I also use a small Schertler Guilia acoustic combo as a stage monitor/DI, with lovely, trouble free results. I think nylon presents a whole different set of problems, and this is my best result yet.
Just installed a James May Ultratonic on my treble nylon (currently tuned at G) so I can do Joni tunings without much capo adjustment on stage. It looks like a 3 element k+k, but John Buscarino swears by them and I trust his ears! I’ll report back when thoroughly tested, but initial tests are promising, with great clarity. Can’t yet say it’s better than k+k though!
One last thought… my ‘85 Guild Mark 3 classical, a lovely clean example I got from Elderley, has no pickup yet. It’s smooth, even, mahogany/spruce sound should be great for vocal accompaniment and I’m going to try a variety of condenser mics first, find a sound I like, and try to match with a pickup that delivers same. Report to follow (might take some months!) I really enjoyed reading all the highly informed opinions here - thanks to all!