Collection Agency matters? How to collect dept successfully?

[Stan C.]

This is my first property and first eviction. 

One of the tenants was sued for non-payment after 2 years of paying with delays but never skipping a payment. Eviction was granted. 3 days before writ of possession (eviction by sherif), COVID quarantine kicked in with maratorium on evictions. If the maratorium is lifted on June 1, 2020 as anticipated, she will ewe 4 months worth of rent. 

My PM will transfer the debt to a collection agency that they work with. 

Questions. Do you know the best collection agency with good dept collection success record? Am I allowed to request my collection agency to take over the one that my PM works with? 

What are overall tips on trying collecting the rent debt?