For me, probably the transaction confirmation times. That is one the biggest wow or attractive factors with bitcoin for myself personally. It is getting too long.
Many of the members here dude! are experiencing the same thing like yours, So I think its not the real problem. So for me my problem in bitcoin is investing in cloud mining.
If you already know that cloud mining is a problem for you then why you still prefer to invest in it, and once you are aware about it then it should not be a problem.