In some situations it may be about a wash. But consider these items;
OWNED MACHINE.
Insurance
Registration/license costs
Other fees (SME registration like in Colorado-Wyoming, air district
registration, etc.)
State reporting requirements (like air compressors, generators, in California)
Maintenance and upkeep (tires, batteries, etc)
Storage room & security
Transportation
Potential or actual lower production
Greater chances of break-down or other maintenance problems on job
Potential for vandalism or other damage
Potential for citations if your machines breaks and hurts someone, or collects DOT
citations for little items not caught in regular maintenance
Have to keep on the books or in the computer for auditing costs and value (more labor)
You won't have all of these with a rental, only some.
If you have an older unit that is a niche machine, that is, one that only does specialized work, and one that happens to be difficult or impossible for a rental outfit to supply in a timely manner, than you might want to consider keeping one around in good condition. That doesn't mean an old high-hour Cat D11 or 651.
You may or may not be surprised at how quickly unused machinery deteriorates. And, at how much work and money it really costs to keep them around if not being used regularly.
If you have a good cost accounting program that will show you exact profit/loss figures, a close study of that, plus some forward looking thought, will give you a pretty good idea of the direction you need to go.
I worked for a guy that also let sentimentality shade his judgment. "Oh, that was my first machine, or, that was the truck that ran over my first wife." If you are the owner, you can make the decision to keep or sell units like these. He kept them, and they cluttered up the yard and occasionally, I'd send one out on a job. The guys on the jobs didn't like the old things, were afraid to run them for fear of mucking them up and facing the bosses wrath, or they just flat wouldn't run them and went off and did without or rented anyway.
I'm sure you will get some other ideas and advice here.
Good Luck!