I don't think that if you rank high or low on a certain map changing map can change much your performance compared to the other players.
Sure some maps are easier and others, let's say Tsunami, much harder if you don't know what to do and some missions can be better suited for some play styles and with certain tanks, ie Banshee is very difficult if you play with some missile tank that lacks of armor and have an offset between the rocket and the aiming reticle as you have often to fire trough little windows and the chance that it hits an obstacle is high, while with that same tank Perseus is a very easy mission as you have open lines of fire, plenty of bushes to hide and make good use of your camo, so your style and the tank you are driving affect how you do in a certain mission.
But on average who performs well in a mission performs well in all them and who don't will not find a magic mission that makes him shine. So as the reward multipliers can go from 2.65 (xp) and 11 (credits) of Ricochet to 4.47 and 22.02 of Leviathan I think that playing the missions with the better multiplier is the most rewarding option both if on average someone performs well or not, the only other thing important is how a mission lasts, a very short one, that you usually complete in a little time, can give the same time/reward ratio of a long one with a better multiplier.
I also think, and this maybe is OT here, that to play every time the same few missions only because are the most rewarding becomes boring, PvE is somehow boring in itself as the bots do the same things every time, the only variables are the tank you are playing and the teammates if you play with randoms, to restrict it only to the most rewarding missions makes it even more boring, transform it in a work where the only scope is the grind while we are playing an online game that will not bring us any glory or money in the RL, our main reward should be the fun we have playing. So while for the tanks that I really want to grind I play at least the time when the first victory of the day is active on a well rewarding map I also like to play most of the less rewarding maps, at least the ones that I have fun playing, I usually skip Ricochet because I don't like it as mission, but as I like Umbrella or Starry Night I often play them if i find them in the queue, even if are low reward ones.