Depends on Race Course and Crew
The choice between the two will depend on the race course and the crew.Closewinded legs: If the course has legs that are close to the wind where the symetrical can't fly, or fly easily but the asymetrical can fly, then the asymetrical is the choice. Leg Length: If the legs are short then this would give the advantage to the asymetrical because of setup and dousing time. If the legs are long then this would give the advantage to the symetrical spinnaker.Number of legs: If you have two or more legs then the symetrical sail must be repacked, taking crew away from sailing for a while. With the asymetrical this isn't nearly as crucial. With two sails you could fly the symetrical on one lap and the asymetrical on the other lap when you're short-handed.Wind strength: If the races are typically in light winds then the standard spinnaker would be best but in heavier winds the asymetrical would be better. On a small boat you don't want the crew running around upseting balance and a sysmetrical spinaker with it's additional equipment that has to be setup and taken down will cause more problems.Crew: If the crew is coordinated and skilled then the symetrical would be good but if you have difficulty with the fordeck crew then you don't want to mess around with a pole and the extra lines, snatch blocks, etc. and adjustments.Wave action: If there are water skiers and power boats creating non-standard waves (not wind waves) this will knock the wind out of your flying sail and make it more difficult to keep trimed. If there are many of these interferences then I'd opt for the asymetrical.Wind shifts: speaking of wind problems, lakes tend to have more fluky winds so if there are major wind shifts (near a point, for example) then an asymetrical would be easier to fly. I've been in situations where I was flying my symetrical and just flying along then ran into a wind line and got hit with a wind from another direction and got back-winded. Not a fund thing.Sail area: the symetrical spinnaker has quite a bit more sail area than the asymetrical and this is the engine that makes the boat go. Since the rules don't distinguish betweent the two the symetrical in combination with a well honed crew and the appropriate conditions will make the boat faster.Ideally it would be good to have both sails in your arsenal.