I have always been a big fan of the "Not less than" speed, either running to the holds or on intermediate/final approach. If you're not going to catch the one ahead, I'll issue a not less than, that way if you want to increase and go quick or slow you can, and I can speed the following accordingly.
It always makes me grin when not much about (and you Midland guys really crack me up with this!), and you issue a "free speed" or "you can increase if you wish" off LAM or BIG on Easterlies, and the response is "OK, here we go................" . Great stuff, and keeps it all moving.
"250kts below 10000, or on the ground..........."