I have tried CHOPCHOP and E-CRISPR-TEST but they gave me different results in terms of genome off-targets for the same sequence! which online tool is the most trustworthy?
I suggest you use multiple online tools, I tried four: Dharmacon, Genescript, Chopchop and invitrogen (not sure if those companies use the same database) and there are more, but eventually I found common sequences which were ranked high as having few off target in multiple tools.