IMO, slide Bone. Not because of the effects described in the preceding post - although some well-placed slides can add to the funk - but because generally the sound cuts better. I've played in, and written for, bands that played classic soul, funk and horn-band stuff (Chicago, BS&T, etc.) and I have always used the conventional Bone in those contexts. Regarding handling "fast funk lines" not quite sure what you mean. Fast feeling (which can mean repeated notes and rhythms) or fast-moving melodic lines? The conventional Bone's not the most agile for fast linear playing until you put it in its upper register, where there are more possibilities for playing in fewer positions and also for using "false" positions. That means that you'll have to work more on the range, than if you might be doing if you stayed with a valve bone, particularly in a standard jazz context.