What is the best antivirus/malware bundle for my iMac

The best antivirus, cleaning app, and overall maintenance app for Mac OS is Mac OS itself. All you need to do with Mac OS to keep it secure and running well is to keep it up-to-date and do periodic (about 1x per week) restarts. Other than that, leave it alone. Adding third party antivirus, cleaning, security and other types of maintenance apps to Mac OS adds no additional level of security. The only thing these apps do is have the opposite affect users want. They make Mac OS slow, unstable, generate odd behavior (much like you are experiencing) and make Mac OS appear buggy. 

Please locate the developers uninstall instructions for Intego and follow to the letter. Then restart in Safe Mode per the directions in Use safe mode to isolate issues with your Mac and then restart normally. 

I will add some thoughts. Macs do not need antivirus apps. They serve no purpose and any of them WILL seriously slow down your computer and will often cause conflicts with other apps. I would go to Intego's web site and download their uninstaller and use it to completely remove Intego. Malwarebytes will not interfere with anything and is highly recommended. EtreCheck is not an antivirus app, but is an excellent program which provides a picture of your computer's operations for review to see what is going on. Both are free.

imho then free malware bytes which one manually run every now and then

and free etrecheck which one run manually every now and then

anything real-time slow down and rarely makes any difference