Lvl 1 Stats

Pros

Strong early game

Massive damage

Great health

Great teamfight engage

Great 1v5 champ

Cons

Bad disengage

Easily kited

Low range

Long cooldowns

Low movement speed

Predictable

AD

AD is the most appreciated stats for Sett since his Q -W -E -R scale with it.

HP

HP is the second most appreciated stat for Sett, his W can deal massive amounts of damage if combined with Overlord's Bloodmail

Movement Speed

Sett lacks movement speed so we have items like Swiftmarch[ , Stridebreaker , Dead man's plate for his speed which could be crucial during a pursuit or a teamfight.

Attack speed

Sett doesn't lack attack speed late game, but in early game it can be a pain if you don't have enough attack speed to kill someone, Sett's basic attack speed is 6.025, by adding Alacrity and Attack speed shard, it goes up to 0.71 at the very beginning.

Lifesteal

Mid stat, Sett doesn't need or can almost never use it during a teamfight, you won't be able to come up to your opponent if you build it first, unless you build it second.

Ability haste

Mid stat, but also is good for his long cooldowns which are reduced by Black Cleaver and Spear of Shojin which add up to 45 ability haste , making it just enough for Sett to gain his Haymaker again in a teamfight.

Armor , Magic Resist

Build it if you really need it against a heavy Magic or AD team comp, mostly your base armor and magic resist are enough, but still might need a bit more from boots.

Tenacity

Mid stat, but is crucial when enemy team has a lot of Crowd Control abilities, like Blitzcrank combined with Syndra, you won't be able to move, you'll be dead faster than you expect to be without Sterak's and Mercury's .