What tools have been most helpful to gather evidence for a SOC 2 audit?

We have had good experience with https://tugboatlogic.com/blog/tag/soc-2-compliance-automation-software/ and moved other compliance workloads in at the same time

Risk Cognizance acts as a central hub, automating and organizing evidence collection to simplify and accelerate the entire SOC 2 audit process. www.riskcognizance.com

Assuming you have some work loads in AWS there are a number of good solutions. I have looked closely at Orkus (full disclosure that I recently was asked to become and advisor). StrongPoint is also one to consider for relevant business applications

For our SOC2 audit we are not using a 3rd party tool for documentation collection. We simply use Excel and a folder hierarchy.

The right person with knowledge and skills in dealing with audits and auditors is more important than which tools to use. The bonus is that the 'right person' will probably know which tools are best suited to what audit.  My opinion only...