Well most of the main players focus on 5v5s, though from what I understand some 1v1s are still played. Most of the average times are for the 5v5s, but even they are usually finished in an hour or less (as in one side clearly gets the advantage and the rest surrender). The main thing holding 1v1 Sins back is that the default 1v1 random map is really quite bad, there are a fairly large amount of planets per player and the map is often divided into two clear halves, often with only the star and/or pirate base connecting them, and they aren't always of equal sizes. Thus if possible try to persuade your opponent to use a pre-made map or even a map designer map.
That said, it is hoped that the new Expansion to rebellion will improve the multiplayer at least a little or and substantially increase the player counts, so if you are truly on the fence it may be best to wait for that. Of course it is at best months away until release, so the old pros are only going to get better in the meantime and you could be getting a lot of experience that could be used against the fresh meat once Rebellion is released.
Further, I advise that the Devs add custom map sharing to Sins of a Solar Empire: Rebellion.
