I've also used lasground_new for general classification, but I tend to use lasground because of this video, where Martin says lasground_new was written for a specific case of an urban area next to mountains. The case that made him create lasground_new was an area in the Philippines.
It's near the beginning of this video:https://www.youtube.com/watch?v=NlwkSv0BuQU&li...
If you read the lasground_new readme file, it only says, "This is a totally redesigned version of lasground that handles complicated terrain much better where there are steep mountains nearby urban areas with many buildings."
But it doesn't say to not use it elsewhere. So it's confusing, and I'm not 100% sure myself.
I had two really difficult "large tree" areas where I spent significant time reclassifying the lidar. Big Basin Redwoods State Park in California had remarkably few ground points under the dense canopy areas. I don't think reclassiying helped much. The other area I had big trouble with was a large tree area north of Wellington, NZ. The problem there was that the limits of the free version of lastools prevented me from improving the original classification. I had to tile at 250m or 500m, and lasground really needed to process across the whole area to produce good results. I can't remember if I accepted the reduction in data lastools imposes when you exceed the point count. I couldn't improve on the original classification done by the professionals. Usually if you have a few buildings classified as ground you can improve on it.
The other place where the free limits were impossible to work around was classifyng ground points in the "dense point cloud" output of drone mapping outputs. There are hundreds or thousands of points per square meter, and you're stuck with a ~250m tile and a bounding box limit that prevents you from having good results---but only in the areas with forest. In lawn areas with trees that don't touch, the results were very good. (I don't remember exactly, but I recall that I used a 300m tile with a 100m bounding box, so only a 100m x 100m tile was the output of running each 300m x 300m tile, and the run time was very long because 8/9ths of each tile was clipped. I think you specify the "clipped size" of the tile and an additional bounding box "border", and lastools won't let you specify a bounding box bigger than the inside. I wanted to run a 64-m tile with a 128m bounding box, and it won't let you. I think I was using a 25m or 50m step, and my theory was you wanted at least 3x the step size as the bounding box---so if you used a step of 50m, you'd want a bounding box of at least 150m. I think I just accepted the loss of data and processed it as one big file.