I would say both ! :attention:
They have both an english interface version, which is good.
Usually Share the fastest one, but the problem is that many files are left incomplete forever. And the search engine is lazy as hell (at least with me). But there are huge file database websites on the web.
With Winny, if you really have the patience, thing will progress steadily through.
But be aware that you need a japanese language support in your Windows OS, else all filenames (including the search engine keywords) will look like gibberish...