Can someone help me know which gun is the best to use if u want to level up fast and get good games with and what attachments to use on it and perks ?
To be honest, I don't think guns have a lot to do with leveling fast unless you want to use them all to complete their challenges. It's mostly about the game mode you decide to play, I think.
Kill Confirmed is where the fast games and big XP is. Some say Search and Destroy is good for XP, but KC allows for bigger scorestreaks and a ton of points .. that's how I see it anyway.
So play some KC and cycle through guns to complete challenges. You should level pretty quick like that.
The gun choice will depend on what your 'categorized playstyle' would be or is. If you're new to the game/COD and haven't yet devoloped a gaming style, then you should try out several guns to see which best fits you.
Kill Confirmed is great for XP if you play the objective (confirms/denies by picking up gold or red 'dog tags') and get a good amount of kills.
Play Hardpoint. Learn where the next Hardpoint is and get there first to capture. Once your team join you, they will likely hold the Hardpoint which leaves you free to gun down the enemy. Stay close to the Hardpoint and you will receive bonus points for your kills.
Good run n gun set up for This playstyle in the playlist is - PDW with Long Barrell and Foregrip. Huge magazine with good range and accuracy. Take a pistol as your secondary to cover the long reload times of the PDW. Perk 3 Wildcard allowing you to run, Extreme Conditioning and Tac Mask together with Flak Jacket. Finish up with C4 and concussion grenade.
Scorestreaks are up to you. Whatever you find achievable. You should score anywhere between 4000-7000 points per game, and you'll be Master Prestige in no time.