Well, I own a 16 Yukon SLT and thoroughly enjoy it, but I havent done much more than a cai but here's my analysis.
Numbers stock:
The SLT with the 5.3 vortec has~355 hp at the crank, assuming a 20-30% loss that means stock you'd have 248.5-284 hp to the wheels.
The Denali with the 6.2 vortec has ~420 hp at the crank, including drivetrain loss you'd have 294-336 hp.
Obviously, stock vs stock the Denali outperforms it in terms of performance.
If you are not able to find an SLT with a 3.42 gear ratio (HD Trailering package), I would definitely go with the Denali. I test drove yukons with the 3.08 & 3.42, the 5.3 with the 3.42 gear ratio is no slouch while the 3.08 leaves much to be desired. The Denali comes standard with the 3.42 gear ratio (if i recall correctly).
If you're able to find an SLT with the HD Trailering package (shouldn't be too hard), supercharging it should easily reach the Denali's crank hp numbers.
For instance, lets take Hennessey's supercharger package crank hp numbers.
508 hp at the crank with 20-30% loss means at the wheels you'd have 355.6-406.4 hp.
However, this Hennessy package costs $10k (or if you look hard enough $6-7k). The price difference between an SLT & Denali with rebates can be a lot less than this.
You have to take into consideration that supercharging the 5.3 vortec will cause strain to the engine, but these engines are robust and have proved how well they can handle power on stock internals. Warranty may also be voided if you go the supercharged route. Lastly, resale value (if you care about it) will worsen rather than improve if it has a supercharger.
tl;dr
Denali
Why?
-If anything goes wrong, warranty is not voided
-Better fuel economy vs supercharged 5.3 (but the economy is bad to begin with so moot point).
-Has exceptional power from the showroom. Comes in a worry free package. Cheaper vs labor + parts charge for supercharging 5.3 vortec.
I haven't included some of the goodies the SLT can't get (mainly stuff I wish mine had) that is standard on the Denali:
HID headlights - Can make this irrelevent on a SLT by using led lights for better lighting. I went with this approach rather than buying retrofitted HIDs.
HUD display
8.1 inch digital cluster display
Magnetic ride suspension
However if you want the above options and a supercharged 5.3 vortec I'd go with a LTZ since its basically a denali minus the 6.2 vortec & 8 speed.