In fact, this isn't even a close call.
Sacks don't tell the entire story, though it is important to note that Watt has totaled 11.5 sacks and is No. 3 in the NFL in this department.
The fact is, when you look at the impact both of these young phenoms have on the game for their respective teams, Watt is head and shoulders above Smith as an overall defender.
Let's take a closer look at how both players impact different aspects of the game.
Vs. the Run
As a five-technique end, Watt is a cornerstone member of the No. 2 rush defense in the NFL—a unit that allows just 85.6 yards per game and that has not allowed a single rushing touchdown all season long.
Pro Football Focus (subscription required) gives him a plus-28 grade for his efforts against the run (the best of any interior lineman in the league), and it's not hard to see why.
The Buffalo Bills—the No. 7-ranked rushing offense in the NFL—only managed to rush for 74 yards against the Texans. We'll use them as an example of how Watt dominates in the trenches vs. the run.
The Bills are in a 1-2 set—one running back and two tight ends—and run away from Watt, who gets immediately double-teamed by the left tackle and left guard.
After the guard disengages, it seems like the tackle still has Watt under wraps, but then a second later we see him running free down the line of scrimmage, where he ultimately helps to bring Fred Jackson down for a loss of one yard.
Watt's incredible strength, burst, lateral mobility and agility—not to mention speed—allows him to absorb a double-team and then run down an NFL running back from the back side. That's unheard of, folks.
Smith is still getting used to playing as a three-down outside linebacker, and though he is freakishly athletic, strong and fast, he still manages to play himself out of position against the run.
PFF gives Smith a plus-5.2 grade against the run, which is pretty good, but it's nowhere near the gaudy plus-28 Watt earned, and it makes Smith PFF's No. 6-ranked 3-4 outside linebacker in this department.
Once Smith learns how to play with more discipline and leverage, he'll become just as adept at stuffing the run as he is at rushing the passer, but for now, he's learning on the fly.
Here is one example of Smith's inexperience as a run-stuffing outside linebacker.
The New York Giants set up in a power-I formation and run right at Smith.
Fullback Henry Hynoski takes Smith on mano-y-mano and blows him up, allowing Ahmad Bradshaw to easily break through Smith's lackluster arm tackle attempt.
Smith gets tricked by the Giants' blocking scheme on this play, thinking the run will go inside, and as a result, he didn't set the edge and allowed Bradshaw to get right around him.
This play ultimately had to be stopped by Donte Whitner and Tarell Brown.
Smith will get better against the run, but for now he's still a work in progress.
Verdict: Watt surpasses Smith against the run at this point in their careers.
Vs. the Pass
We already touched on the fact that Watt is easily the best lineman against the pass, as he's totaled 11.5 sacks through 10 games.
That's unheard of from a 3-4 defensive end. To put this in perspective, Justin Smith and Calais Campbell were considered to be absolutely dominant when they put up 8.5 and eight sacks, respectively, in their career-best years.
But Watt isn't a one-trick pony against the pass.
He's earned the nickname "J.J. Swatt" due to his incredible ability to bat down passes at or near the line of scrimmage. And who can forget about his insane pick-six against Andy Dalton and the Cincinnati Bengals in the playoffs last year?
So not only is Watt affecting the passing game as one of the NFL's most dominant pass-rushers, but he's having the same kind of impact as some of the league's top cornerbacks.
As an outside linebacker, Smith has different responsibilities than Watt against the pass.
Although he doesn't often drop back into coverage, Smith does occasionally play in space on passing downs, and quarterbacks have found him to be an easy defender to exploit.
PFF finds that out of the nine times quarterbacks targeted Smith, he allowed seven catches for 55 yards, including 41 yards after the catch. Those quarterbacks have a passer rating of 129.2—the third-worst mark of any of the 3-4 outside linebackers graded.
As it is with Smith against the run, his ability to cover in space is still a work in progress.
That said, his pass-rushing skills are top-notch, as his 15 sacks through 10 games clearly shows.
Even more impressive is the fact that Smith has totaled 10.5 sacks in the past four games.
Clearly he's on fire, but that doesn't mean he is better against the pass than Watt.
Verdict: Watt has a bigger impact against the pass than Smith at this point in their careers.
It's easy to get caught up in the hype of the moment.
Smith has turned up the heat in a major way the past four games, sacking opposing quarterbacks 10.5 times.
However, playing defense in the NFL encompasses so much more than just tallying sacks, and Watt clearly surpasses Smith as an all-around defender at this point in their young careers.