It depends very much upon the type of issue you are pursuing through court. My suggestion would be to go to
CanLii and search for cases similar to yours. Then start looking at the case - who argued it, were they successful.
In order to
get into Court an attorney has be decent - Immigration cases are only heard after a successful application for leave, which itself must be persuasive. To win cases an attorney has to be very good. Finding someone with experience in your type of case is actually very important.
I did that in my own JR application - I reviewed the cases and picked an attorney with a good track record. His filings in my case were successful (leave granted) but I ultimately discontinued the case after CIC agreed to grant me PR in my second application - an application that was processed in record time. I maintain that this was because CIC's attorney concluded they were likely to lose.
But my case was of a very specific type (medical inadmissibility) and there are only three lawyers I'd recommend for such cases.]
Other attorneys are likely to be similarly qualified in other classes of case - but pick the best for your type of case.