discrete solid state mainly ie. mosfets, jfets, transistors even well done high end opamps is more to my taste. tubes can sound good if done well, but still not really my thing especially for source. better for amps and such so you can choose to have the colour or not. I know thats a bit of a cliche, but until big dollars are spent on tubes I do find they colour the sound
transformers are a funny one, I have enjoyed well implemented transformer coupled dacs before (including my own), but once you know what a mess they make of the signal it becomes a bit less appealing. can sound quite good, musical, easy on the ear, euphonic etc, but distortion isnt great and normally neither is DNR. can sound good though, but from a technical standpoint, if that matters to you as it does me, its a bit of a turn off.