When you order goods from China, the Yanwen package will be delivered to China Post and will be delivered to you via the standard, unofficial China Post Air Mail service.
So, if you have a choice between Yanwen Logistics and China Post, don’t worry too much, it almost doesn’t matter what you choose, you will get the package through China Post.
All in all both services are reliable and you don’t have to worry about purchasing a shipment, on the most famous ordering site from China both of these services are free, so if you have these two options it doesn’t matter which one you choose.