Depends what I'm answering.
If it's my mobile, I usually just say, "Hello?" Apparently, I sound like I'm surprised I'm getting a call when I answer. Usually because I am.
When I'm answering the phone at work, I have to do a small speech. "Hello, [my store] where you can trade in your old games for new/now pick up Ghostbusters/we have 25% off pre-owned games, Sarah speaking, how can I help?" The number of people that hang up after the first word is staggering. But mystery shoppers look out for that sort of thing.