Hi. In the past, started with world coins (especially German states, Indian states, Chinese provincial, the more obscure the better). US type, Roman & Greek ancients, tokens and the like. Nowadays mostly stack PMs and sometimes US Mint issues (I think this upcoming March of Dimes set will be good) with flipping in mind. I like the ATB Ps, and I do think they'll be very good in the future, but @ 67 years now, it better start pretty soon!
How about yourself?