Ginn is intriguing purely because of the tease of being a duel threat of returns and catches from Brees (he'll be running Brandin Cooks routes but without the hands). I wouldn't be that excited that he'll put up stellar return numbers. He'll be switching from a non-dome to home dome stadium, so touchback % will be a concern. He is moving within the same division (with kickers with good touchback %). I think you can expect his return yards last year to be his baseline/ceiling for this year.
Solid sleeper picks for return yards are slim, but here is my list:
Offensive positional players:
Tyler Ervin - Houston - RB
-- His return skills was a reason he was draft because the Texans were trash at it last year.
Cordarrelle Patterson - Oakland - WR
-- I think Patterson has better upside than Ginn for being a duel threat. Oakland has a great O-line. He is moving from a dome stadium to open air stadium. Amari/Crabtree will have the focus of the stronger DBs with Patterson running through the slots. The main concern is that Jalen Richard is also good at returning, so I don't fully trust the return job is his.
Defensive positional players:
Marcus Sherels - Vikings - CB
-- Will be replacing Cordarrelle Patterson as their punt/kick-off returner.
Adoree Jackson - Titians - CB
-- Same reason for Ervin with Houston
The highest ceiling of all sleepers:
Jabrill Peppers - Browns - S
-- I think this guy will have the biggest splash in return yards of everyone. Starting rookie QB resulting is a lot of change of possessions resulting in more scores/kickoff returns. Defense in the beginning stages of becoming good. Whole division plays in outdoor stadiums (in cold weather) resulting in less touchback kickoffs. Slotted for both punt & kickoff return duty.