most of my shares are rare, and go to those who browse me, so I set for 20 slots per person (95KB/s allocated total). This gives the quick browser who only want s to check out a few files 40KB/s, which is fast enough for them to decide if they want more. If they do want lots, they can still get 20 at a time at a decent rate.

The usual advice I've seen is set your slots to upload a minimum of 5 KB/s each.

Also, if you run for high uptimes, consider the monthly ISP limits. Mine likes us to stay below 60 GB/month, so if my files are getting too popular, I'll remove the ones that are already out there and give the less known files more of a chance (while easing my monthly rate). I recall one person saying they like to rotate shared folders weekly.