I like moly grease. Moly is great for metal to metal anti friction.
It's handy to get some for general purpose lubrication at the home/shop.
You can consider first burnishing/polishing the splines. Scotchbrite, steel wool, wire brush on a drill, etc. This will get rid of minor machining imperfections [disc and input shaft].
Also, lube the throwout bearing and shaft it rides on. Don't forget the clutch fork pivot and whatever else moves.