re: Best 2017 Rookie Class in the NFL so far

Comparing Lattimore to Colston, you have to consider the positions they play.

Colston was a very reliable large WR, with a HOF QB throwing him the ball. Keep in mind that playing with Brees made Lance Moore and Willie Snead 1000 yd WRs. They get production, but nobody would argue that they are at or near the top of their position in the league.
Colston was "merely" Brees' favorite target at the time. He continues to put up 5000 yds passing a season without him, just as he has done without Jimmy Graham.

Lattimore is playing corner on a team that doesn't have an elite pass rush, and he's been matched up against some good WRs. He isn't just filling a hole on defense (like you could say about, say, Jason David in a Tampa 2 scheme), he's blanketing guys and taking them out of the game.

You can (and the Saints have) remove Colston from the offense and it will click along. You can't remove a top corner from the defense without the team having to change things significantly.

Only time will tell if Lattimore continues this, but as of right now, I'd say he has a bigger impact on the game.