Would have been nice if Mars Telecommunications Orbiter [1] had flown. In addition to a higher orbit more suitable for communications, it would have included an experimental high-bandwidth laser link to Earth. Alas, the project got cancelled for budgetary reasons.

[1] http://en.wikipedia.org/wiki/Mars_Telecommunications_Orbiter

Wouldn't just a higher orbit achieve the same thing? You'd be in sight for longer periods, right? Without locking you into a location the way synchronous would.

The current orbiters are primarily for imaging, so it makes sense that they're as low as possible. If you were always going to have several surface missions, it might make sense to have higher orbiters primarily tasked with communication relay.

As someone explained to me on another thread, the orbiters they have now are in polar orbits. A more equatorial orbit would create very frequent uplinks.

One thing is that they didn't know Gale Crater was where they were going to land until pretty soon before launch. There were a number of other sites. And if they chose one further from the equator, that satellite wouldn't necessarily be in the right place.