I'm looking for a medium to moderately high tension set (lower string action) that provides a very smooth feel, and "better than average sustain". ( As flatwounds go...)
The medium to high tension is not where they excel but you'd be hard pressed to find a string that is smoother than TI Jazz flats. Regarding the decay the TI's are also great because they are not like other flats. They have good sustain and do not thump. They really are very unique.
GHS or Fender flats. My 4+ year old GHS Precision flats have so much sustain, I have to mute them between notes and will easily ring out for three or four measures. My fairly new Fender flats are much the same way, but on a different bass. Playing whole notes is easy.