Bust coins - - Why collect Bust coins? First, they're historic. These coins were minted from 1792 to 1839, a period at the beginning of the country's independence, and a 1795 half dollar may have been spent by Thomas Jefferson, and it is rumored that the silver for the 1792 half dismes came from Martha Washington's silver set. All but four dates were made at the Philadelphia Mint. (Those 4 coins are the 1792 half disme and disme, and the 1838-O and 1839-O half dollars.)  Second, they have individual characteristics. Each die pair (referred to as a "die marriage") has been documented, and many collectors attempt to collect all of the die marriages in their chosen set. Plus, there are die cracks, some of which lead to part of the die falling out, which leaves a raised area called a "cud" on the coin. Some coins with cuds are rare and can be quite valuable. Third, they are rare. The 1909-SVDB cent is often called "rare". But in less than one year, you could buy enough to have a roll of them. There are several Bust coins for which if the entire quantity in existence is put together, it would not make up a roll. Now that's rare. 

Seated coins  - - I have spoken to a lot of collectors working on sets of Liberty Seated coins, and they all use the word "challenge" to describe what it's like to try to complete a set of Liberty Seated coins. Try to find all the coins needed for a Seated dime set, or a quarter set, or a half dollar set, or the Seated dollar set.  Compared with the Bust series, the minting process is more consistent, so the quality of the coins is better. Seated series have so many die pairs that it is virtually impossible to collect them all, so many collectors work on a date and mint set, with or without some of the major varities in the series.  Every series of Seated coins has its "impossible" coin. The 1870-S half dime is unique (only one known), as is the 1873-CC No Arrows dime. The 1873-CC No Arrows quarter has 5 or 6 known. The 1853-O No Arrows Or Rays half dollar has 4 known. And the 1870-S dollar has 11 known. The top graded of each of these coins except for the 1873-CC NA quarter is valued at over $1 million, in my opinion. Even if you should be fortunate enough to have the financial ability to purchase such a coin, you might have a long wait as most of these coins are tightly held in collections and are not likely to be available for some time.  EXCEPT FOR NOW, because we have one of the four known 1853-O No Arrows Half Dollars for sale now!  With only 4 known, when will you get another opportunity like to acquire this coin?