From a cost standpoint, the beginner will find it least expensive to collect used stamps, much more costly to save unused issues, and most expensive to go after mint copies. That general statement is usually, but not always, true. In a few cases, a certain used stamp may be more expensive than its mint variety, but those instances are quite uncommon.
Many great collections consist of used stamps only.
Many collecting purists prefer the used specimens, based on the premise that stamps are created to move mail. To those collectors, a stamp without a cancel has never fulfilled its reason for existence. Many great collections consist of used stamps only. Used stamps are more plentiful than mint copies. You will have more to choose from, and they are easier to find.