I think it's too close to call as to who is in the best position right now.
In theory, you could say Nintendo still has the success of the Wii and the handheld market behind them, but from everything I've heard the WiiU isn't shaping up to replicate its success. Sony had huge success with Playstation 1 & 2, but had some pretty lean years during the last console cycle. Microsoft is difficult to judge because it's always just been kind of a middle of the road contender and I can't say that I think they're trying to be anything else, but they also lack a strong international focus in their marketing. The Xbox is not a truly international brand in the way that Sony and Nintendo genuinely try to be with their consoles and brands.
Personally, I think the Xbox One has fallen behind in the race for a number of reasons. Firstly, latching onto television even though television is kind of a dying medium. Secondly, calling a press conference that only gamers would be interested in watching and talking about everything other than games. Thirdly, again, targeting a games console at people who aren't interested in games during a press announcement that nobody except gamers were watching or interested in. Fourthly, basing their whole marketing strategy on appealing to this idea that people who aren't interested in playing games will want to buy a games console for its non-gaming functions. Even the Wii with its huge and wide-reaching mainstream appeal never sold itself as anything other than a games console; it sold because it had all these titles and casual games that audiences who don't usually play games were interested in. But I digress.
Overall, I really can't predict at this point who's ahead, and probably won't be able to until after E3, but I'd say that I'm anticipating that it's going to be much more of a two-horse race between Sony and Nintendo unless Microsoft has a dramatic turnaround.