Consider Your Typical Winds
Both David and Bruce have good comments and make valid points. It'd be really nice to have both a symetrical and an asymetrical sail but if you have to choose. The symetrical/traditional spinnaker has more square footage and therefore could provide more power, but... If the winds in your cruising area are typically astern, and not much in the way of powerboat wakes, then the traditional spinnaker can make sense. I find the powerboat wakes really mess up the sail unless the wind is blowing pretty good. If the wind angle if often abeam or forward of abeam, or varies a lot, then the asymetrical can make sense.The traditional spinnaker, in my opinion, takes more time to set up, with a pole, topping lift, and fore guy, and takes more effort to fly. How much into sailing and sail trim is your mate? It isn't a sit back and relax kind of sail and it's what I'd call more labor intensive to fly. With the asymetrical one doesn't have to mess with as much gear so if you have a short distance I think you'd more more likely to fly it. We fly a traditional chute so unless there is a reasonably long run I tend to err on the side of not flying it.Some of our most memorable sailing experiences have been while flying the chute. One afternoon we ran for several hours at up to 10 knots through the water on a H-35 sailing double handed - great time - my wife still remembers that and it was 8 years ago.Personally, I'd like both sails. Tough decision but I'd call it a win-win either way! By the way, you already have a feathering prop, right?