Saito!

Yes the O.S.'s are good engines, but you wouldn't believe how tolerant the Saito is of mis-tuning!

I've seen people complain that the Saito's consume more fuel, when they haven't realized that the engines they based this on, were completely mistuned, often with the needles as much as 11 turns out from optimal!... yet the plane still flew just fine!

The Saitos also tend to be much ligher than the O.S. engines.