The Nova .21 will probably give you the best fuel mileage and with OK power and very easy to tune.
A Picco .28 like the LRP is going to be the most power.
The OS VG has some real durability issues. Great motor when new but don't last as long as most others.
Avoid the STS at all cost.
Some other recommendations would be the RB S3 or S5 or maybe a Go Tech. I haven't tried the Go's myself but I here they run pretty well.