Part 1 - Basics + Attachments
Part 2 - Assault
Part 3 - Engineer
Part 4 - Support
Part 5 - Recon
Part 6 - PDWs
Part 7 - Shotguns
Part 8 - Pistols

Note about the bipod: While this attachment may seem clear to use with a long range rifle, it's not as good as you may think. For bolt-action rifles in particular, the changes to recoil and spread don't mean much of anything, because there's such a long time between shots. It steadies the rifle for you, but you already have the breath holding button for that. Learn to use it! Against other snipers, this lets you dodge their shots before you sight in your own. For a semi-auto, it's better because it will help with recoil and spread, but only if you plan to take multiple shots at a time.

Recon:

SVD + MK11 + M39 EMR: Semi-auto rifles - I'm putting all three of these together because of how similar they are. Same damage, RPM, mag size, recoil, and spread, only real differences are in bullet velocity and reload speed. Unfortunately, as with the previous Russian starting weapons, the SVD comes in last, and is thus not recommended. The choice between the other two is more difficult, as the MK11 has the faster reload speed (by .4 seconds, or 1 second when reloading from empty), and the M39 has the faster bullet velocity (by 20 meters/second). I don't actually know how that small a difference in velocity would affect accuracy at range, but it will help at least a little. Because of this, I'd suggest to only use the M39 to players that want a semi-auto rifle for use at longer range, and to use the MK11 at short range to make use of it's great reload speed (which can still be useful in long range engagements). Attachment selection is fairly simple, decide what range you want to be best at, and choose the appropriate scope. Note that the foregrip for these three weapons helps vertical recoil by a small factor as well, which doesn't matter at all if you are taking your time between shots. So I'd take the bipod for range, and the foregrip for up close engagements. Additionally, the suppressor helps with recoil and spread, but lowers damage and bullet velocity at range, so I'd take it on close to mid range setups.

SKS: Semi-auto alternative, faster firerate & bigger mag - Compared to the other semi-auto rifles, this is worse in a number of ways. It has lower damage per shot (34-30 instead of 50-34), lower suppression, much slower bullet velocity, worse horizontal recoil, and a reload speed slightly worse than the M39. It is also the only Recon rifle to have an initial spread when firing while aiming and not moving. It's low, but it's there, so really long range accuracy is going to be even harder on top of the low bullet velocity. To compensate for all this, it has a ~50% faster fire rate, a twice as large magazine, better vertical recoil, and a lower initial spread when moving or firing from the hip. To me, the key to this weapon is to fire as quickly as possible, as you can put out two rounds before the other semi-autos can, and if you don't take advantage of that you are missing out on your strength. I wouldn't suggest using this rifle at longer than midrange, but if you insist, a bipod is essential to help with the spread. I'd probably personally attach a holo/red dot, foregrip, and maybe a flashlight, and try to be really aggressive with it. (Note for hardcore players: While the SKS does less damage, it still takes the same amount of shots as the other semi-auto rifles to kill: one headshot or two body shots. The only time the other rifles will possibly be better is if you shoot them in the legs and/or they are already partially damaged.)

SV98 + M40A5: Bolt-action rifles - These rifles sport the higher 75-55 damage with a lower firing speed, lending themselves to careful shots. Of the two, the M40A5 is better for those that like to shoot a lot, or just at a closer range. It has the faster firing speed, and the faster reload speed from an empty mag. On the other hand, the SV98 lends itself a little better to slower, perhaps longer range play with more consideration between shots, with a better bullet velocity, and better reload speed mid-magazine. Ultimately, they are more similar than they are different, and either could work in any situation.

M98B: Bolt-action alternative, high damage & bullet velocity - The most powerful rifle in the game, it does a whopping 95 damage at close range, which drops to 59 damage at 75 meters. It also had the best bullet velocity of any Recon rifle, making it the easiest to hit with. As expected, the time between shots and the reload speed is higher than the other bolt-actions, but not by terribly much. You only get 5 rounds in a magazine, half as much as most other rifles, which could be an important factor. For long range engagement, there is no greater weapon in the game than this.

Recon, Back to Karkand:

QBU-88: Bad semi-auto - I'm not sure what this is for. It's identical to the MK11, except it has a reload speed a second longer AND it has much lower suppression for some reason. This doesn't seem worthwhile to me at all.

L96: Great overall bolt-action - This rifle combines the good parts of the first two bolt-actions, by combining the M40A5's firing speed with the SV98's bullet velocity (and beating it!) The downside is the reload speed from empty, it's as bad as the SV98. If that's not a big issue to you, then I would definitely choose this over either of them.

Man, I'm really behind schedule. I've been busy with traveling some, and the Steam winter sale didn't help any with keeping my free time free. PDWs, shotguns, and pistols are all that's left. They are all pretty quick, so I might blow through them all in one or two days on this coming weekend.

Thanks for all the support in the comments, I always appreciate it. And feel free to point out any errors.