What are some image board alternatives to 4Chan?
Some image board alternatives to 4chan include:
1. 8kun (formerly known as 8chan)
2. Lainchan
3. 420chan
4. EndChan
5. Kohlchan
6. iChan
7. AnonIB
How much are they used in comparison? Do they have illegal content / very controversial members? Are they legal in the US?
None of the other image boards listed receive as much traffic as 4chan.
8chan is known to have users post content that has violated US and international law in the past.
These Image boards do not have membership however controversial individuals such as Patrick Wood Crusius have posted on 8chan in the past. 
None of these image boards are illegal in the US.
Who is Patrick Wood Crusius?