jdupes very easy and extremely fast.
jdupes is a program for identifying and taking actions upon duplicate files such as deleting, hard linking, symlinking, and block-level deduplication (also known as "dedupe" or "reflink"). It is faster than most other duplicate scanners. It prioritizes data safety over performance while also giving expert users access to advanced (and sometimes dangerous) features.
# Search a single directory:
# Search multiple directories:
jdupes directory1 directory2
# Search all directories recursively:
jdupes --recurse path/to/directory
# Search directory recursively and let user choose files to preserve:
jdupes --delete --recurse path/to/directory
# Search multiple directories and follow subdirectores under directory2, not directory1:
jdupes directory1 --recurse: directory2
# Search multiple directories and keep the directory order in result:
jdupes -O directory1 directory2 directory3
# EXclude files over 1M, sumarize info, recursive
jdupes -X size+=:1000k --summarize --recurse ~