Definitely bypass. Way more versatile. Bypass loppers are way better on green wood. They say that anvil is better for dead wood, but you only really notice it on fairly large very dry branches. I have both, and I hardly ever use the anvil loppers. My favourite are the Fiskars 18" bypass with the PowerGear. I think it's model # 96256946. The gearing really does give it all the poer of the longer loppers - more, in fact -- and at 18" it's short into to throw into your pack for trail building.
Another great tool is the Fiskars 6" pruning saw with the blade that slides back into the handle. Model # 96836989. It fits perfectly in the pump port on a camelback, and it's great when you run into some deadfall across the trail. It has an agressive tooth pattern that slices through anything up to about 3" in seconds, and you can use it to take out stuff up to about 6" in diameter, though it takes a bit longer.
I know there are a few people on here that have some extensive use of loppers. I am compiling my list for Santa and am wondering whether you would recommend bypass or anvil style loppers? Looking for something to use around the home for tree cleanup and out on the trail to help with those early season trail days.
Thanks for your help.