I want to claim the honor of starting the first ever completely pointless "Versus" thread on the GOG forums which can never see adequate resolution through debate and serves primarily as a vent for fanboy propaganda!
AND NOW, YOU MUST DECIDE WHO THE VICTOR WOULD BE!
This is a face-off between gaming's two great masters of stealth! In the first corner, we have...

Garrett, "Master Thief":
Trained by the ancient mystical society of the Keepers in the ways of stealth, combat, and basic rune-magic, Garrett is a man who no bars can hold, no door can bar, and no wall can stymie. Capable of blending into the shadows with nearly supernatural skill, Garrett can become nearly invisible in the shadows. On top of that, his arsenal includes a sword (or dagger, maybe...), a bow with a wide array of special magic arrows, and an assortment of miscellaneous gadgets including health-restoring potions, flash bombs, explosives, holy water, and much, much more!
Garrett has survived in the City by his wits and his skills at remaining hidden for many years. His unique talents have also saved the city from destruction multiple times. Garrett is a good fighter and a great thief, but is he impressive enough to take on Fisher?
Sam Fisher, "SIGINT Ninja":
A veteran of decades' worth of wars and black ops, Fisher is a covert infiltration specialist for NSA's secret Third Echelon program. Fisher is legendary for his ability to strike unseen deep into enemy territory, complete his objectives (ranging from assassination to data collection), and escape undetected. Clad in black latex and kevlar, Fisher can make himself look like the ghost of shadow when he needs to. On top of that, he is armed with the latest in tactical espionage technology; goggles that have night-vision, thermal-vision, and EMP-vision, two silenced guns, a variety of special projectiles for those guns (mostly for making non-lethal takedowns), and a variety of toys of varying lethality to defeat any obstacle he faces. However, Sam's most powerful weapon might be his information: through his sub-dermal implants, he can communicate with his allies at Third Echelon, getting intelligence and backup from them on demand.
Sam Fisher will fight any foe on America's behalf, but will fight even harder to protect (or avenge) his only daughter, Sarah Fisher. He's single-handedly prevented WWIII many times, but can he beat prevent Garrett from shooting him in the back?

Sam has thermal vision and as far as I remember, Garrett can't elect to make himself cold at will.

However, Garrett has a mechanical eye that he can use to peer around corners or set up traps with. Plus, he can go more places with rope/vine arrows or the climbing gloves in DS. Fisher is restricted to pipes or wall ledges.

Sam Fisher has the Land Warrior rifle. Obviously he wins.

The way I figure it, Sam has the edge in most situations because he can counter most of what Garrett does. Garrett can't walk away unseen from Fisher under any conditions that wouldn't leave them both blind, because of Fisher's goggles. Garrett might be able to run and climb faster in order to escape, but that won't being him victory. Garrett's bow is not really a match for Sam's guns.
Garrett might be able to win in a melee battle with Fisher, but from what I've seen Sam Fisher has a helluva lot more muscle than Garrett (what with his abiliity to hang from pipes on the ceiling, pick up people on the floor, and strangle them), so Garrett's only advantage is his relative mobility.
However, these guys are both stealth-fighters. The real question is not "who wins in a fair fight" so much as it is "who is more likely to get the drop on who." Sam Fisher's array of detection instruments still give him an advantage in this area, but Garrett is in a better position to lay traps (magical or otherwise) to take Fisher out without confronting him directly. I wouldn't put it past Garrett to fill a house with mines and oil, lure Fisher inside, exit the house, and then launch a fire arrow into the house to blow the whole place up.

This is of even more importance.
God damn it, Garrett wins hand down. This thread is over.

Remember, these guys are all about staying silent an unseen. Wouldn't Garrett getting more google hits mean he loses?

Duly noted.
SAM FISHER WINS!

Thats weird, I see Sam Fisher winning over Garrett.

Garret has the advantage because its a single word whereas sam has the match 2 words.
The only really fair way to do it is this way in which sam wins (or loses if the stealth angle is played)
http://www.googlefight.com/index.php?lang=en_GB&word1=Sam+Fisher+Splinter+Cell&word2=Garrett+Thief

Garret, because besides being the coolest rogue ever to grace the PC, he has to do all his sneaking without the benefit of Fishers' pansy high-tech gadgets(in the first game anyway), AND he has to face off against the supernatural.

Garrett has killed zombies, ghosts, walking mechanical death machines. He has survived having his eye ripped out of his head, and hes never even come close to being killed. To top it off I heard that Altaïr Ibn la-Ahad and Ezio Auditore da Firenze both have night-terrors involving a dark hooded figure that slits there throats while they sleep.
Sam Fisher sometimes ignores missions objectives, does his own thing. Sometimes doesn't even care about stealth and sorta just runs around and does what he wants. And hes a driven man motivated by revenge and his sole purpose is to kill. Yay goggles, yay weapons... he has to sleep sometime eh?
Garrett is all about the mission and getting it done at all costs.... Period.... Oh and he defeated an old angry god... Yeah, a GOD couldn't defeat Garrett.

I never played Splinter Cell, but I know I loved the Thief series, so here's a vote for for Garrett.

Oh, and Garrett also doesn't have a giant glowing green square on his back at all times.