Preston Fairmont, favors crystallized via an old shotgun

Preston's stats require an advanced deck. The designers definitely pointed builds into very specific directions - favor events that require no tests, Fire Axe or Old Shotgun (if you even have a weapon) with Dark Horse or Well Connected. With this deck, each game will be complex as one engine will start helping take over for weaknesses in other engines not yet developed (shotgun/reflexes vs double double/small favor, double double/intel report vs investigation using well connected boosted by Faustian Bargains) with Delilah and Lola getting in some actions and soaking.

First, let's talk about weapons, cuz Preston has so little options: Fire Axe is easily the best starting weapon for Preston. However, this is no Dark Horse deck, so he will quickly grow out of it. Bats and Sledgehammers are not very efficient. Timeworn Brands (cricket bats) are boring and cost way too much resources and XP. Old Shotgun is the only non-Illicit firearm he can have, so we need to work around its 0 ammo condition. Old Shotgun will stay in play and get two ammo when you use Swift Reflexes, Sleight of Hand, or Friends in Low Places (if upgraded for it). Friends in this deck concentrates on Well Connected and Double Double, because those are both key to the deck. We don't want to water down the Favor events that Antiquary doesn't work with. Swift Reflexes used as an attack is by far more versatile than Sleight of Hand, and perfect since the inheritance can buy these extra actions for other purposes in emergencies, thus Swift Reflexes is the primary ammo source for Old Shotgun and should be grabbed from discard with a Double Double Scrounge for Supplies loop after each battle. This will only do 3 to 6 damage, to 1 to 2 targets, so you'll still need Favor events. Elusive is a great card, but Decoy allows you to stay for other actions and is better with Crystallizer. After two shotgun blasts, there's a good chance you can finish them off with Delilah or a Small Favor.

Soak: Since we're focusing on one weapon in the deck, backpack is a must. Since there can be no Underground Market, we don't have room for Lonnie and Heavy Furs (a healing engine). We need another source of soak. Talisman of Protection keeps you from losing by 2, is gained with Backpack, easily scrounged, and only takes an arcane slot, but prevention isn't active soak. Leo is cheap to upgrade to (and an extra action is high priority) but his high cost stops you from building your resources as quickly. Peter Sylvestre is great for soak since he has some horror healing and costs 3. You can build up free actions with Delilah O'Rourke and Lola Santiago which also boost your stats.

General XP upgrade order: Charon's Obol (if solo), Versatile (adding 2 Ward of Protection if not taken by another investigator, else Lucky!), Money Talks to be replaced soon, and one Talisman of Protection), upgrade both Well Connected, Delilah O'Rourke (replaces one Money Talks), Charisma, Lola Santiago (replaces the second Money Talks), Charisma, Double Double (replaces a Drawing Thin), upgrade Friends in Low Places with the Ritual trait for 2 XP, Old Shotguns (replace Fire Axes, use Scrounge for Supplies with Double Double to return a Swift Reflexes to your hand), one Antiquary (replaces the second Drawing Thin), one Salvage (replacing a Peter), for a total of 39 XP.

With more XP or another campaign: Counterespionage (replaces Ward of Protection/Lucky!), upgrade Backpacks for smoother starts, Ace in the Hole (replaces a Swift Reflexes), then upgrade Friends in Low Places a lot. Precious Memento is very good, but only for soak so not as versatile as allies. The Red Clock is good too, but the XP cost is high.

Mulligans are more complex than normal: Double Double and Well Connected (or Friends in Low Places to find them) come first, and you should be aggressive with a mulligan if you don't get any of those 3. If you have at least one of those, Fire Axe or Small Favor, Backpack, Trial by Fire, and an ally are worth keeping.