Dragons... maybe about 20-25 and my character is in low 30s level range.
Giants? Killed at least 40 of them by now, and likely twice as many Mammoths, usually together in groups. That's a fight that will push you more then a dragon. I raid their camps often since they are a fun challenge. Oh and the Unrelenting Force Shout fully powered is SOOOOO satisfying using it on them. After all the times they have sent me flying or stumbling, its fun to send them flying and tumbling over for a change.