I use Rotosound RS66LD but I add an additional high string to put on my 5stringers which I get separately. So it goes 35 45 65 80 105. When I string up the 5stringers for the baritone songs it's almost the same gauge but RS665LD, 45 65 80 105 130. They are always roundwound. I can't stand the sound or moreover the feel of flatwounds. I learned on flats in orchestra class on double bass (standup bass, upright bass, acoustic bass whatever), and I hated them then too. The rounds on a fretless neck take so long to make damages that it's almost not worth worrying about. Every fretless neck I have is ebony wood and it's hard enough to take the rounds. I've never taken out any frets to convert over, the one bass that I did put together I bought a fretless neck from Fender, so I have no experience with removing frets. I started on that homemade Fender wannabe, then got a Carvin for a while, which I still use often, but then got a nice assorment of ESPs...not LTD fretless.
*For the record...Human was recorded with my old Black Rickenbacker 4001 (fretted) and Individual Thought Patterns with that homemade Fender wannbe 4string (fretless).
I like the songs on the new Sadus album that I recorded with the fretted ESP so much that I've been writing more and more for the fretted one again. I'll always try to use either one that gives me the best sound for the song, but now that I have the double neck it's getting more interesting to switch between frets and fretless within the same song! It's a monster, but if properly weilded it can make it a lot more convenient switching between the different sounds between the two different kinds of neck.
Any more string/bass questions...? Think I covered it all. But if not...fire away...!
SDG