9 on some, 9.5 on others, 10 on Gibsons, 10 or 11 on my Jaguar, 11 or 12 on acoustic. Don't have anything strung with Flatwounds at present. Nothing down-tuned.
9 right now because I accidentally bought a box of a dozen 9 gauge string packs. Hopefully I'll burn through them soon and I can move on to 10's or 11's. Never been a huge fan of lower gauge strings.