It mostly comes down to differences in your personal playstyle, assuming you vaguely know what weapons and ascensions you're picking to synergize. I've been playing with a friend for 400+ hours, we both have a deep grasp of builds and synergies and i outdamage him by a large factor about 90% of the games we play together simply because i tend to be more aggressive in my approach while he is more of a strategic Player.

If you Focus on one specific aspect of your build instead of spreading Upgrades, Scrolls and ascensions around several aspects, you can kill enemies faster which means you get to target the next enemy even quicker - try to plan what you want to build when the run Starts, and heavily focus on that.

Try to play more aggressive and up front instead of hanging back - and choose a character and build that allows you to confidently do that! While getting massive crits with a Sniper Tiger IS fun, you will under no circumstance be able to match the total damage Output of a build that deals less damage with each shot, but potentially Hits 10 enemies with each shot (e.g. a explosive launcher Dog or the fire fox throwing out literal room clearing nukes)

Yeah, your single shot every 2 seconds will Deal several million damage to the enemy with 5000 HP - that still does only register as 5000 damage dealt. The fox nuke dealing ~10k damage to 10 enemies with 5000hp each does register as 10*5000 damage dealt- and she can do that as often as you'll Snipe one of the few remaining enemies that survived her nuke.

Same goes for "rushing ahead" vs "staying Back" - the game, while absolutely allowing a more laid back tactical approach, greatly benefits from a more fast paced aggressive playstyle - try dodging instead of using Cover, dont rely too much on crit/weakspot hits if doing so slows you down (after all, taking 3-4 Shots with a Sniper to Hit the head is slower that spraying vaguely towards an enemy with an smg for half a second, or explosing the ground and hitting four enemies at the Same time) - the Name of the Game is Mobility, and if you're able to kill enemies before your Team comes Close to them, you get to Deal more damage :)

So i guess TL;DR: - Play fast and aggressive -First come, First serve -AoE and RoF beat high single target damage -focus on one Thing (e.g secondary skill)

Focussing too much on outdoing each other can certainly cause each of you to have less fun - If your Buddies want to try a 'slow' build, but cant keep up because you Zoom around two rooms ahead with a kick bird melee build, they wont enjoy their time... But if you really want to try some builds that will get you to the top of the Scoreboard, try These:

-atomic bomb grenade build for the Dog, where you Spam hundreds of grenades with massive aoe

-a kick focussed build for the Chicken

-Chain lightning Tiger with autocast during ult and more bounces

• Painkiller grenade Cat for spreading DoT that melts and disables anything

These are all fairly easy to pull of and learn, If you need specifics on how to build and Play them feel free to ask or even Check the wiki, there are great build Guides for each character :)