People that usually get involved will eventually find their "niche" so to speak... best to grab a good amount of all denominations early and then decide what you like the most.
You usually get the most "bang for your buck" with Halves, provided you can find a bank that has them or that can order them for you - best to build a relationship with a bank over the course of time before doing this though. Nickels have done me really well through the years - War Nickels
, key date Jeffersons in high grades, proofs, Buffaloes, V nickels
, and even varieties like the 1943/2 P are out there. Dimes can be fun, but you really need A LOT of patience with them - silver is still out there, believe it or not... Cents, while fun, rarely get you really nice finds - the 1998 Wide AM is out there, as is the 1970-S Small Date if you're persistent and out West... Quarters would probably be the least appealing thing for a newbie because they represent your lowest probability of finding a silver coin out of any of the denominations. The "W" mint marked coins are usually the main focus of most people's searches, along with the modern ATB
coins. Also, several of the 2009-2012 dated Quarters are tough to find thanks to lower mintages.
CRH Nickeloholic. 1,300,000 nickels searched in five years! Already have found THREE complete Jefferson sets!