Now keep in mind as I share these loadouts, I'm not saying I am right and everyone is wrong. These are my personal choices as to what I prefer and think works best from my 5 years of attempting to be a decent sniper main.
This first loadout for it's primary is the stock sniper rifle, looking around on the internet and here on steam it is clear that stock is a favored weapon for casual game play, it's easy to use, and straight forward, as simple as it can go, just like my vanilla ass.
for the secondary you have the jarate for you kinky weirdos. It's an item I got early on in the game and has helped me a ton when it comes to those sneaky soulless spy crabs trying to steal my mortal soul.
To top off the jarate we have the bushwacka. After topping someone off with your mobile micurate, you can run up to them and start slashing away. The jarate will cause you to do mini-crits on them, but with the bushwackas secret mousekatool, those mini-crits become full on crits.
This loadout is great for handling pesky spy crabs, annoying lime scouts, and... well maybe not Heavy's with a pocket medic, but you can certainly take on that medic.
;)

Now with this second load out, it's not what most people would consider optimal, but I've used it for more of an offensive kinda strategy, for the few times I'm willing to get down and dirty.
For the Primary weapon I chose the Sydney Sleeper!
The Sydney Sleeper of course can cause the same effects as some good ol' Jarate, nothing special on it's own, but stick with me here.
The secondary is the infamous Darwin's Danger Shield, this gives you an extra edge by giving you 50% resistance against burns and makes you immune to the effects of after burn, so you can chase away those pyros, or if you got the balls, pull up on a heavy who's packing The Huo-Long Heater.
Now for your melee weapon we go back to our handy dandy Bushwacka!! When you scope someone up close with your Sydney Sleeper they have the affects of Jarate which allows you to crit them with every hit.

Okay, okay, I admit... those last two are similar, cause they both utilize the Jarate effect, so I'll do us both a favor and make myself seem more credible and less biased, so you can show off my guide to all your friends.
This loadout uses different effects starting with our primary!
I lied, the primary is the old rootin tootin classic stock rifle. It's a simple and yet loved weapon and the more I've played the more I realize it truly is a good weapon to play as casually as I do. So go back to your roots and don't be afraid to be basic, it's the first step of being a great sniper main.
For our secondary we have a trustworthy Razorback! With your razorback equipped you won't have to worry as much about spies cause it will make them think twice. Don't forget to cherish your beloved Razorback while you can, because he sacrifices his life to save yours and alert you of the danger you were almost in.
This is where your melee weapon comes into handy. Once you've realized a spy crab jsut stabbed your best friend you'll use that anger, take your Tribalman's Shiv and show him what's up. When he's out of arms length you whip out your sniper and pop a cap in his cap.

Are you still reading this guide? Wow, you must really want to be a good sniper main. Well I'm not the best but I certainly hope that my guide helps someone get a decent start on their journey... maybe my next guide will be tips and tricks. Well, this is the last loadout I have for y'all, it's nothing special but one I personally find super fun to use.
For my main I got a hated weapon called the Huntsman, or otherwise known as the Lucksman... I'm not 100% sure why, but I think it's just cause they're mad I got a head shot on them from across the map on turbine or 2 Fort. It's just challenging to use, especially when two or three other sniper are using normal rifles.
With my secondary I use the Cozy Camper backpack. This will constantly be healing you after you take any sort of damage, this is good for when you get attacked up close, you can run away and have a little better of a chance to get away safely.
And last but not least is the melee weapon, which is the not so comfy and nice Tribalman's Shiv. Now hopefully they'll run, and if they don't you might have to duke it out with them and hope your Cozy Camper helps you become the ultimate victor before you get shot by that soldier you sniped out of the air a few minutes back, who's just been waiting to get the edge on you.