The Resistance map works best. When you start you can run around and just kill people so you can buy a Predator Drone Missile and any Light Machine Gun ( M60, LMG etc.). That way you can take out both!

At the start of wave seven you should each have a Sentry Gun! Go to the house in the middle of the map. Put your sentries at each door and sit next to your Sentry, that way you have double guarding.

Just shoot them when they come in! When the Juggernaut comes kill him with Airstrike or a Predator Drone Missile.

Do the same routine with the Sentries until wave 15. Then, it's 2 Juggernauts. You can both take them out with the Airstrike and Predator Drone Missile.

Now you should both be able to buy Riot Shield Squads! They will form like a human wall around your doors! You're safe in your house and when they all die just buy them again!

Do the same with your Sentries. Your weapons should be any Light Machine Gun and a Striker.

Wave 19 there is three Juggernauts. Eliminate 2 of them with the Airstrike and Predator Drone Missile etc.

For the third Jauggernaut one of you should equip your Striker and the other his M60. The player with the Striker should go towards the Juggernaut and shoot him in the face. The other should take advantage of this distraction and shoot him in the back!

Keep on buying Sentries and Riot Shield Squads. Now you both should buy Claymores and set them up in and around the Door.

Wave 20, this is when shit hits the fan. Do the same routine with the Sentries and Riotshield Squads.

Note that with almost every wave after 20 there is Choppers. You know the drill by now - Predator Missile and M60! But save the Chopper for last.

Do the same stuff with every wave on (Juggernauts, Choppers etc.).