JIRA had R4J plug-in that is pretty good if using jira doesn’t upset you. I’ve used it and it works nicely. You get traceability “for free”. There’s additional plugins to enable testing so you can do full requirement to test in JIRA (along with work breakdown if you like that sort of thing). I like JIRA for this because you can put all the conversation about each one in the comments. Gives extra color to the reasoning.

JAMA is a great tool I demoed but couldn’t get the org to buy.

Doors is crap.

I recommend word/ excel if you have <60 requirements. If you have more than a tool like above helps, esp if you need to have traceability to testing.