If at all???? :-) Sorry its not eggnog in my book if it ain't spiked. The safe choice is your common Bacardi light rum. But the Myers or another good dark rum would be better. Wikipedia says brandy, moonshine, or whiskey... moonshine? Hmm... I'd vote the rum definitely.
Spiced rum is hard to beat in eggnog! But equal parts Jack Daniels and Crown Royal also works nicely, if you want it to have a real kick. Captain Morgan is great for the spiced rum, but Firefly Sea Island Spiced Rum is my personal favorite. I typically add homemade flavor-infused simple syrups too. I'm a huge fan of spiked eggnog during the holidays :-)