Take different champs (cars) for different maps, depending on what you want to do. For Cursed Necropolis take a transporter because they will start first and have the greatest chance of grabbing the bomb first, i like the little monster for that one. For Heavy Metal Arena, i usually take an interceptor because there's a lot of room to deal a lot of damage and help your team win, i prefer Wildfire for this one. For the Temple of Sacrifice i'd take a support, like Photon. Now this is all situational. The perfect 4-man team i've found working the best is: 1 Transporter, 2 Interceptors and 1 Support, so you will have to think accordingly of the current game you are playing.