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.
yeah, it's also my biggest problem, especially when I really need money to buy something

then I have to wait for miner to confirm my transaction, but I think it depends on your lucky and today I just need less than 30 minutes for the confirmation

If you use blockchain, you can send bitcoins even if the transaction is not confirmed. I agree that it takes time but if you need bitcoins urgently, you can ask the sender to add a high fee so that it gets confirmed soon.