I currently use AVG Free. I want to get paid antivirus and tune up software. PCMag recommends McAfee Antivirus and iolo System Mechanic. Does it make a difference if I buy programs from differenet companies, or should I buy both from the same company, such as AVG Ultimate?
Doesn't make a difference what so ever as they both do different things. Getting it from one place may just put it under one roof.
However as most would, I would tend to advise to stay away from TuneUp software, as nearly anything they can do, you can do yourself in windows, and some of the other stuff they do (such as registry cleaners) can cause more harm than good. Avoid them.
Some other good AV have the whole package in one, with AV running and general PC maintenance tools included in one software package - such as Bitdefender.
Avoid system tune-up software like the plague, and most particularly anything that says it's a "registry cleaner."
What version of Windows are you running? If Windows 8.1 or Windows 10 I'd strongly suggest you take a look at the built-in Windows Security. Windows Defender/Security has consistently been in the top tier for several years now.
See the most recent plus the last several years of historical test results from: