Many sites (including Dropbox, and this one from time to time) are blocked in China, not because they have sensitive content but just because the criteria for blocking sites is so broad. This means that there are many services I can’t use, not least FTP to my own website.
The best, most pain free option I’ve found is Transfer Big Files. The maximum files size is 30mb and you have (I think) a monthly limit of 20gb.
The other option is Baidu’s cloud service. Here you can transfer 2g files.