Seated H10s and standing liberty quarters. And I must admit I'm a sucker for higher grade Indian head cents.
I don't really have a "favorite" I like all old US coins for some reason or another. I'm still trying to find something affordable and nice in the late 1700s.
Back in 1976ish I was digging in my parents back yard and came across this buried probably 2-3 inches below the grass Which actually started my coin collecting at some point I bought this to compliment the 1925
I_can_say that, two days from now, my favorite coin series will be Lincoln Cents. For one day, anyway.
I like Morgans and coins with history, like the 1861 O half with three different minting authorities.
For US coins Seated anything. 5/3 Dollar gold is growing on me fast though. For world coins, Sovereigns and Australian 1D and 1/2D. Though any foreign gold will catch my interest.
Roman Republic pre-denarius didrachmae (280-211 BCE), Roman Republic Aes Grave, Roman Republic litrae. Modern: Flying Eagles, Trade Dollars, Odd-Denoms. Gold
In descending order- Buffalo 5c Flying Eagle 1c (too bad they replaced it with the Indian 1c so soon) Select foreign doubled dies Mercury 10c Walking Lib 50c Peace $1