Contacts and Google and which to use or lose?

Over the past couple of months I have found that the contacts app is using far too much CPU (and CPU time) trying to sync both my Google contact list and separately, my iCloud contact list. (Like many, my email address is also my Apple ID/iCloud address. And that address is a front for my gmail account).

I would say 90% of the contacts are duplicated between iCloud and the Google accounts. But I cannot figure out how to combine them into a single group. Note that I assume having fewer contacts will reduce the CPU load and hence save my battery trying to sync all these other contact lists. (I also understand that syncing Google contacts can draw more CPU than iCloud or others... Which is how I first noticed this, since it was draining my battery overnight while the Mac was sleeping.)

Questions:

1. Would it be better to store all my contacts in iCloud? Since they’re already on both my Mac and my iPhone, and I assume I would still be able to pull them up as a part of sending an email or placing a phone call? Or,
2. Should I try to keep them all over in Google, since I use Gmail 99% of the time and do not use iCloud mail much at all.
3. Of course, the following question: How would I merge these contact lists together?

Looking for advice and help and thank you in advance.