ACS. Best way to get all PUMA, all variables, all years?

The American Community Survey (ACS) began large-scale surveying starting in 2005, and began nationally-representative population surveying in 2007 (when it included group quarters populations). Prior to that, the ACS was inherited from the Decennial Census Long Form. Essentially, your data years would look something like this: 1990, 2000, 2007-2018. The microdata are available in the Public Use Microdata Sample (PUMS) series. These PUMS have substate geographic delineations known as PUMS Areas (PUMA's) that are divided to cover a minimum population threshold for each PUMA. As a result, PUMA boundaries change every 10 years and are often not comparable to each other between Decennial Censuses. This may greatly affect your ability to compare 2010 with 2000 or 1990 if your goal is substate analysis, for instance.

If you wish, you can find most of the non-spatial data through IPUMS. They also have the geographic boundaries through their NHGIS project. Registration is free for these platforms.