There's nothing wrong with investing in coins it's just unwise for most people. I try to avoid areas where there's much investing going on because it's important to me to either make money or at least not lose much money on coins. But investors have as much right to buy and/ or enjoy coins as much as anyone else.
I don't really focus on one series/denomination in particular. I buy what catches my eye at that moment. I never really got caught up in trying to complete a particular series, I don't know why but it's just not my thing.
I've always liked collecting coins that are 40,90,or .999 silver. I cannot afford gold at this point in time. I figure that I will always have some sort of valued commodity no matter where I am in the world. But since you asked, Liberty half dollars got me started and next American Silver Eagles also Morgan dollars. They are affordable and they all have the best coin designs, IMO. But always make sure you research thoroughly before making major purchases and get yourself a "Redbook".
Buffalo nickels because that is what I was given by grandparents when I was younger and I was always impressed by the design. Truly original design -- no prior U.S. coinage really comes close to it. Both sides have so much to recommend them -- lots of strike issues, small details to look for to determine how full the strike is. And then there are all the issues with the color -- originality, tone and luster. My advice would be to pick one or two series and study up before spending too much. Good luck!
I would have to say for US coins the Ole reliable Morgan Dollar is a winner. Its pretty and still available for reasonable prices. Traci
I mostly collect modern gold commemoratives, circulated silver dollars, and a variety of silver bullion items. I've been looking for something to take me to the "next level" but so far haven't found the right coin or coin series. I've come close to starting an Eisenhower dollar collection a couple of times but there's something holding me back.