Well, they're not truly polar. The "best" orbit for Mars is with inclination of -86 degrees where, due to the vagaries of orbital mechanics and Mars' gravity, the orbit precesses automatically to follow the Sun through the martian year (This is known as "sun-stationary"). I believe that Odyssey and MGS are in orbits such as this, but with subtle differences such as the local time at which they cross the meridian. (I vaguely remember that MGS crosses at about 2 pm which gives near-vertical lighting and rather "flat" looking images, while Odyssey crosses at about 4 pm, but I could be wrong here)

The ESA craft is in a distinctly elliptical orbit with rather different behaviour - it isn't sun-stationary and precesses from nightside to dayside to allow nighttime radar work - if only the radar wopuld work! :-)

The Vikings were in less inclined orbits, as I remember, but this is something a little research could clarify. Unfortunately, I'm in an airport terminal right now and although I have a nice free wireless connection, my flight will be called before Icould look all these things up, so how about someone else doing some homework?