I always have and probably always will. Just tried Urban Chaos with Jake and got a score of 39000. Anyone got any tips for this map or just some general tips for mercenaries?
get all time while ignoring enemiesm, kill enemies with headshot > melee combo for +5 seconds each kill (or counter kills if you can worth 10), shoot green hourglasses when there are plenty of enemies on screen, only go for gun kills on purpose if you need to save combo... get 150 kill combo get million points! :D
Well I myself have only managed an A rank once and normally a B rank, but the consensus is usually spend your first minute or so running around grabbing the 6 (I think) time bonuses, you'll get up to around 7-8 minutes with all of them.
Then start doing headshot+melee combos, always try to kill with a melee for the time bonus and good scores can only be accomplished by racking up large combo kills, it takes like a combo of 50 just to get a A-B rank. So keep the combo going no matter what, even if it's a non-melee kill.