There are mainly 2 types of Pu'er Tea in the market.  Raw (Sheng Pu'er) and Ripe (Shu Pu'er).  Which one should you buy depends solely on personal preference.

Raw (Sheng Pu'er)- is a pu'er that is made from non-fermented green tea leaves that were picked, quickly roasted, sun-dried and then steamed to be compressed into round disks called cakes. After which the cakes are stored and aged until the tea’s taste is properly transformed.

Since raw pu'er doesn’t go through the piling process, it retains a fresh scent as well as a little bit of a sweet aftertaste.  It is mellower, smoother and provides a more complex flavor the longer it ages.  The color of the brew is golden yellow to burnt orange, depending on the age of the tea.

Raw Pu'er can be consumed immediately to enjoy its fresh, floral flavors or they can be stored and aged like red/white wine.  

Ripe (Shu Pu'er)- is pu'er that is made from fermented tea leaves. It goes through the same steps as the raw pu'er. However, at the stage of producing the cakes it undergoes a procedure, called ‘wet piling’. The leaves get piled up to a certain height, then it gets wetted with water, and covered by a linen cloth. This allows the tea to stay warm and creates a humid environment to accelerate the fermentation. After the tea ferments to a certain degree, it gets unpiled and ventilated.

Ripe Pu'er  have an earthier and mellow taste. As it ages, it becomes smoother and the earthy flavor shifts into sweet plum flavor.  The color of the brew is deep red or dark brownish.

Ripe Pu'er preference is to consumed immediately; but can be stored as well.  However the taste will not alter as much as Raw pu'er during the storing process.  

Pu'er tea in different years  https://www.f-tea.com.tw/en/product.asp?pds=1&pcat=35&pcat2=55

pu-erh loose tea https://www.f-tea.com.tw/en/product.asp?pds=1&pcat=68&pcat2=78