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.
Yup. If you need it done fast, use dogecoin as an example. I've sent stuff with tx fee, and it took over 6-7 hours....just the time to find a block. etc, etc. A lot of people dont think this is a problem, but its a huge problem.
Using an altcoin is not the solution. I send my transactions always with a 10K satoshi fee. The transactions confirm within 2 blocks. It's that simple. To be even more sure, you must add 1000 satoshi's per KB. Then you are mostly fine.