Newtones are an interesting issue in this discussion; they are made as low-tension strings, so you can play heavier gauges without putting as much stress on the instrument. I have some fairly fragile older guitars, and Newtones are first choice for those. For mandolin, the heavier the better for me; I like the way they drive a carved top, and I like a string that 'fights back; a bit when playing tremelo. Heavy pick, of course, but that's another discussion...
Tim