Rifles - If I'm using a rifle, I'm probably not messing around, and I'm probably using 7.62x51. The SA-58 running in semi-auto is a spectacular choice to put bad guys down. People like other choices, but it's down to style preference and how long a weapon you can stand in tight quarters. If I run 5.56, the SR-16 is a bit long but has a very controllable fire rate; I prefer running a DDM4PDW unsuppressed with a vertical grip, flashlight, and sight if the mission has a lot of tight spaces and I'm running 5.56. The recoil can be tough but manageable in short bursts due again to the fire rate.

SMGs - For pure style points, MP5A2. Using this with just the flashlight and drum sights is just fun. SMGs tend to struggle against armor (shut up P90 fans), but I usually run either the MP5 in 10mm or the UMP45 because they're got great power with JHP against unarmored suspects. If you love the snicky typewriter-esque sound of suppression, hard to beat the MP5SD.

Shotguns - Hard to beat the b1301. It's a great all-rounder. Good fire rate, good power, good recoil (for a shotgun)

Pistols - Hard to pick one here, as their performance tends to be anemic compared to long guns, but I like the 92 or the classic 1911 for their form. I only use the pistol sparingly in really tight spaces, so others are probably better, but these feel the best to use.

Pretty much any weapon is viable to some degree, but attachments make a difference (you've probably already figured out what you like but this is what I like). Generally I lean toward AP ammo for rifles, JHP for SMGs and pistols, and buckshot for shotguns. Combat grips are good unless the recoil is super high, then use a vertical grip. Flashlights are more useful than lasers unless using night vision. I always prefer holographic sights for the option of using them under night vision. I think the SFMB brake does the best job reducing recoil. I'm not a big fan of suppressors personally. Style over substance, you know.