It's too close to call IMO.
Audi have their strengths - efficiency, knowledge, some speed but not the outright pace, reliability.
Toyota have really grown into the series - their car is extremely fast, and so far reliable - but 6 hours is different to 24 - if it stays together, I think they'll win.
Porsche were blindingly quick on certain corners at Silverstone and Spa - but reliability has to be their potential issue. They're also not QUITE up to speed with the team side of pit stops etc - but I suspect this will be ironed out by the time we hit the big race.
Overall, I think any of the three manufacturers could win it - for me though, it's likely to be Toyota, Audi, Porsche based on previous races.
I love the fact that it's too close to call!